mv std libs to library/

15 files changed, 0 insertions, 8854 deletions

diff --git a/src/libstd/sync/barrier.rs b/src/libstd/sync/barrier.rs
deleted file mode 100644
index 01314370ce3..00000000000
--- a/src/libstd/sync/barrier.rs
+++ /dev/null
@@ -1,215 +0,0 @@
-use crate::fmt;
-use crate::sync::{Condvar, Mutex};
-
-/// A barrier enables multiple threads to synchronize the beginning
-/// of some computation.
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::{Arc, Barrier};
-/// use std::thread;
-///
-/// let mut handles = Vec::with_capacity(10);
-/// let barrier = Arc::new(Barrier::new(10));
-/// for _ in 0..10 {
-///     let c = barrier.clone();
-///     // The same messages will be printed together.
-///     // You will NOT see any interleaving.
-///     handles.push(thread::spawn(move|| {
-///         println!("before wait");
-///         c.wait();
-///         println!("after wait");
-///     }));
-/// }
-/// // Wait for other threads to finish.
-/// for handle in handles {
-///     handle.join().unwrap();
-/// }
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Barrier {
-    lock: Mutex<BarrierState>,
-    cvar: Condvar,
-    num_threads: usize,
-}
-
-// The inner state of a double barrier
-struct BarrierState {
-    count: usize,
-    generation_id: usize,
-}
-
-/// A `BarrierWaitResult` is returned by [`wait`] when all threads in the [`Barrier`]
-/// have rendezvoused.
-///
-/// [`wait`]: struct.Barrier.html#method.wait
-/// [`Barrier`]: struct.Barrier.html
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::Barrier;
-///
-/// let barrier = Barrier::new(1);
-/// let barrier_wait_result = barrier.wait();
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct BarrierWaitResult(bool);
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl fmt::Debug for Barrier {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.pad("Barrier { .. }")
-    }
-}
-
-impl Barrier {
-    /// Creates a new barrier that can block a given number of threads.
-    ///
-    /// A barrier will block `n`-1 threads which call [`wait`] and then wake up
-    /// all threads at once when the `n`th thread calls [`wait`].
-    ///
-    /// [`wait`]: #method.wait
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Barrier;
-    ///
-    /// let barrier = Barrier::new(10);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new(n: usize) -> Barrier {
-        Barrier {
-            lock: Mutex::new(BarrierState { count: 0, generation_id: 0 }),
-            cvar: Condvar::new(),
-            num_threads: n,
-        }
-    }
-
-    /// Blocks the current thread until all threads have rendezvoused here.
-    ///
-    /// Barriers are re-usable after all threads have rendezvoused once, and can
-    /// be used continuously.
-    ///
-    /// A single (arbitrary) thread will receive a [`BarrierWaitResult`] that
-    /// returns `true` from [`is_leader`] when returning from this function, and
-    /// all other threads will receive a result that will return `false` from
-    /// [`is_leader`].
-    ///
-    /// [`BarrierWaitResult`]: struct.BarrierWaitResult.html
-    /// [`is_leader`]: struct.BarrierWaitResult.html#method.is_leader
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Barrier};
-    /// use std::thread;
-    ///
-    /// let mut handles = Vec::with_capacity(10);
-    /// let barrier = Arc::new(Barrier::new(10));
-    /// for _ in 0..10 {
-    ///     let c = barrier.clone();
-    ///     // The same messages will be printed together.
-    ///     // You will NOT see any interleaving.
-    ///     handles.push(thread::spawn(move|| {
-    ///         println!("before wait");
-    ///         c.wait();
-    ///         println!("after wait");
-    ///     }));
-    /// }
-    /// // Wait for other threads to finish.
-    /// for handle in handles {
-    ///     handle.join().unwrap();
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn wait(&self) -> BarrierWaitResult {
-        let mut lock = self.lock.lock().unwrap();
-        let local_gen = lock.generation_id;
-        lock.count += 1;
-        if lock.count < self.num_threads {
-            // We need a while loop to guard against spurious wakeups.
-            // http://en.wikipedia.org/wiki/Spurious_wakeup
-            while local_gen == lock.generation_id && lock.count < self.num_threads {
-                lock = self.cvar.wait(lock).unwrap();
-            }
-            BarrierWaitResult(false)
-        } else {
-            lock.count = 0;
-            lock.generation_id = lock.generation_id.wrapping_add(1);
-            self.cvar.notify_all();
-            BarrierWaitResult(true)
-        }
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl fmt::Debug for BarrierWaitResult {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("BarrierWaitResult").field("is_leader", &self.is_leader()).finish()
-    }
-}
-
-impl BarrierWaitResult {
-    /// Returns `true` if this thread from [`wait`] is the "leader thread".
-    ///
-    /// Only one thread will have `true` returned from their result, all other
-    /// threads will have `false` returned.
-    ///
-    /// [`wait`]: struct.Barrier.html#method.wait
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Barrier;
-    ///
-    /// let barrier = Barrier::new(1);
-    /// let barrier_wait_result = barrier.wait();
-    /// println!("{:?}", barrier_wait_result.is_leader());
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn is_leader(&self) -> bool {
-        self.0
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::sync::mpsc::{channel, TryRecvError};
-    use crate::sync::{Arc, Barrier};
-    use crate::thread;
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn test_barrier() {
-        const N: usize = 10;
-
-        let barrier = Arc::new(Barrier::new(N));
-        let (tx, rx) = channel();
-
-        for _ in 0..N - 1 {
-            let c = barrier.clone();
-            let tx = tx.clone();
-            thread::spawn(move || {
-                tx.send(c.wait().is_leader()).unwrap();
-            });
-        }
-
-        // At this point, all spawned threads should be blocked,
-        // so we shouldn't get anything from the port
-        assert!(matches!(rx.try_recv(), Err(TryRecvError::Empty)));
-
-        let mut leader_found = barrier.wait().is_leader();
-
-        // Now, the barrier is cleared and we should get data.
-        for _ in 0..N - 1 {
-            if rx.recv().unwrap() {
-                assert!(!leader_found);
-                leader_found = true;
-            }
-        }
-        assert!(leader_found);
-    }
-}
diff --git a/src/libstd/sync/condvar.rs b/src/libstd/sync/condvar.rs
deleted file mode 100644
index 9b90bfd68b5..00000000000
--- a/src/libstd/sync/condvar.rs
+++ /dev/null
@@ -1,818 +0,0 @@
-use crate::fmt;
-use crate::sync::atomic::{AtomicUsize, Ordering};
-use crate::sync::{mutex, MutexGuard, PoisonError};
-use crate::sys_common::condvar as sys;
-use crate::sys_common::mutex as sys_mutex;
-use crate::sys_common::poison::{self, LockResult};
-use crate::time::{Duration, Instant};
-
-/// A type indicating whether a timed wait on a condition variable returned
-/// due to a time out or not.
-///
-/// It is returned by the [`wait_timeout`] method.
-///
-/// [`wait_timeout`]: struct.Condvar.html#method.wait_timeout
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-#[stable(feature = "wait_timeout", since = "1.5.0")]
-pub struct WaitTimeoutResult(bool);
-
-impl WaitTimeoutResult {
-    /// Returns `true` if the wait was known to have timed out.
-    ///
-    /// # Examples
-    ///
-    /// This example spawns a thread which will update the boolean value and
-    /// then wait 100 milliseconds before notifying the condvar.
-    ///
-    /// The main thread will wait with a timeout on the condvar and then leave
-    /// once the boolean has been updated and notified.
-    ///
-    /// ```
-    /// use std::sync::{Arc, Condvar, Mutex};
-    /// use std::thread;
-    /// use std::time::Duration;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move || {
-    ///     let (lock, cvar) = &*pair2;
-    ///
-    ///     // Let's wait 20 milliseconds before notifying the condvar.
-    ///     thread::sleep(Duration::from_millis(20));
-    ///
-    ///     let mut started = lock.lock().unwrap();
-    ///     // We update the boolean value.
-    ///     *started = true;
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// let mut started = lock.lock().unwrap();
-    /// loop {
-    ///     // Let's put a timeout on the condvar's wait.
-    ///     let result = cvar.wait_timeout(started, Duration::from_millis(10)).unwrap();
-    ///     // 10 milliseconds have passed, or maybe the value changed!
-    ///     started = result.0;
-    ///     if *started == true {
-    ///         // We received the notification and the value has been updated, we can leave.
-    ///         break
-    ///     }
-    /// }
-    /// ```
-    #[stable(feature = "wait_timeout", since = "1.5.0")]
-    pub fn timed_out(&self) -> bool {
-        self.0
-    }
-}
-
-/// A Condition Variable
-///
-/// Condition variables represent the ability to block a thread such that it
-/// consumes no CPU time while waiting for an event to occur. Condition
-/// variables are typically associated with a boolean predicate (a condition)
-/// and a mutex. The predicate is always verified inside of the mutex before
-/// determining that a thread must block.
-///
-/// Functions in this module will block the current **thread** of execution and
-/// are bindings to system-provided condition variables where possible. Note
-/// that this module places one additional restriction over the system condition
-/// variables: each condvar can be used with precisely one mutex at runtime. Any
-/// attempt to use multiple mutexes on the same condition variable will result
-/// in a runtime panic. If this is not desired, then the unsafe primitives in
-/// `sys` do not have this restriction but may result in undefined behavior.
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::{Arc, Mutex, Condvar};
-/// use std::thread;
-///
-/// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-/// let pair2 = pair.clone();
-///
-/// // Inside of our lock, spawn a new thread, and then wait for it to start.
-/// thread::spawn(move|| {
-///     let (lock, cvar) = &*pair2;
-///     let mut started = lock.lock().unwrap();
-///     *started = true;
-///     // We notify the condvar that the value has changed.
-///     cvar.notify_one();
-/// });
-///
-/// // Wait for the thread to start up.
-/// let (lock, cvar) = &*pair;
-/// let mut started = lock.lock().unwrap();
-/// while !*started {
-///     started = cvar.wait(started).unwrap();
-/// }
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Condvar {
-    inner: Box<sys::Condvar>,
-    mutex: AtomicUsize,
-}
-
-impl Condvar {
-    /// Creates a new condition variable which is ready to be waited on and
-    /// notified.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Condvar;
-    ///
-    /// let condvar = Condvar::new();
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> Condvar {
-        let mut c = Condvar { inner: box sys::Condvar::new(), mutex: AtomicUsize::new(0) };
-        unsafe {
-            c.inner.init();
-        }
-        c
-    }
-
-    /// Blocks the current thread until this condition variable receives a
-    /// notification.
-    ///
-    /// This function will atomically unlock the mutex specified (represented by
-    /// `guard`) and block the current thread. This means that any calls
-    /// to [`notify_one`] or [`notify_all`] which happen logically after the
-    /// mutex is unlocked are candidates to wake this thread up. When this
-    /// function call returns, the lock specified will have been re-acquired.
-    ///
-    /// Note that this function is susceptible to spurious wakeups. Condition
-    /// variables normally have a boolean predicate associated with them, and
-    /// the predicate must always be checked each time this function returns to
-    /// protect against spurious wakeups.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the mutex being waited on is
-    /// poisoned when this thread re-acquires the lock. For more information,
-    /// see information about [poisoning] on the [`Mutex`] type.
-    ///
-    /// # Panics
-    ///
-    /// This function will [`panic!`] if it is used with more than one mutex
-    /// over time. Each condition variable is dynamically bound to exactly one
-    /// mutex to ensure defined behavior across platforms. If this functionality
-    /// is not desired, then unsafe primitives in `sys` are provided.
-    ///
-    /// [`notify_one`]: #method.notify_one
-    /// [`notify_all`]: #method.notify_all
-    /// [poisoning]: ../sync/struct.Mutex.html#poisoning
-    /// [`Mutex`]: ../sync/struct.Mutex.html
-    /// [`panic!`]: ../../std/macro.panic.html
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut started = lock.lock().unwrap();
-    ///     *started = true;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// let mut started = lock.lock().unwrap();
-    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
-    /// while !*started {
-    ///     started = cvar.wait(started).unwrap();
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn wait<'a, T>(&self, guard: MutexGuard<'a, T>) -> LockResult<MutexGuard<'a, T>> {
-        let poisoned = unsafe {
-            let lock = mutex::guard_lock(&guard);
-            self.verify(lock);
-            self.inner.wait(lock);
-            mutex::guard_poison(&guard).get()
-        };
-        if poisoned { Err(PoisonError::new(guard)) } else { Ok(guard) }
-    }
-
-    /// Blocks the current thread until this condition variable receives a
-    /// notification and the provided condition is false.
-    ///
-    /// This function will atomically unlock the mutex specified (represented by
-    /// `guard`) and block the current thread. This means that any calls
-    /// to [`notify_one`] or [`notify_all`] which happen logically after the
-    /// mutex is unlocked are candidates to wake this thread up. When this
-    /// function call returns, the lock specified will have been re-acquired.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the mutex being waited on is
-    /// poisoned when this thread re-acquires the lock. For more information,
-    /// see information about [poisoning] on the [`Mutex`] type.
-    ///
-    /// [`notify_one`]: #method.notify_one
-    /// [`notify_all`]: #method.notify_all
-    /// [poisoning]: ../sync/struct.Mutex.html#poisoning
-    /// [`Mutex`]: ../sync/struct.Mutex.html
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    ///
-    /// let pair = Arc::new((Mutex::new(true), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut pending = lock.lock().unwrap();
-    ///     *pending = false;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// // As long as the value inside the `Mutex<bool>` is `true`, we wait.
-    /// let _guard = cvar.wait_while(lock.lock().unwrap(), |pending| { *pending }).unwrap();
-    /// ```
-    #[stable(feature = "wait_until", since = "1.42.0")]
-    pub fn wait_while<'a, T, F>(
-        &self,
-        mut guard: MutexGuard<'a, T>,
-        mut condition: F,
-    ) -> LockResult<MutexGuard<'a, T>>
-    where
-        F: FnMut(&mut T) -> bool,
-    {
-        while condition(&mut *guard) {
-            guard = self.wait(guard)?;
-        }
-        Ok(guard)
-    }
-
-    /// Waits on this condition variable for a notification, timing out after a
-    /// specified duration.
-    ///
-    /// The semantics of this function are equivalent to [`wait`]
-    /// except that the thread will be blocked for roughly no longer
-    /// than `ms` milliseconds. This method should not be used for
-    /// precise timing due to anomalies such as preemption or platform
-    /// differences that may not cause the maximum amount of time
-    /// waited to be precisely `ms`.
-    ///
-    /// Note that the best effort is made to ensure that the time waited is
-    /// measured with a monotonic clock, and not affected by the changes made to
-    /// the system time.
-    ///
-    /// The returned boolean is `false` only if the timeout is known
-    /// to have elapsed.
-    ///
-    /// Like [`wait`], the lock specified will be re-acquired when this function
-    /// returns, regardless of whether the timeout elapsed or not.
-    ///
-    /// [`wait`]: #method.wait
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut started = lock.lock().unwrap();
-    ///     *started = true;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// let mut started = lock.lock().unwrap();
-    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
-    /// loop {
-    ///     let result = cvar.wait_timeout_ms(started, 10).unwrap();
-    ///     // 10 milliseconds have passed, or maybe the value changed!
-    ///     started = result.0;
-    ///     if *started == true {
-    ///         // We received the notification and the value has been updated, we can leave.
-    ///         break
-    ///     }
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::sync::Condvar::wait_timeout`")]
-    pub fn wait_timeout_ms<'a, T>(
-        &self,
-        guard: MutexGuard<'a, T>,
-        ms: u32,
-    ) -> LockResult<(MutexGuard<'a, T>, bool)> {
-        let res = self.wait_timeout(guard, Duration::from_millis(ms as u64));
-        poison::map_result(res, |(a, b)| (a, !b.timed_out()))
-    }
-
-    /// Waits on this condition variable for a notification, timing out after a
-    /// specified duration.
-    ///
-    /// The semantics of this function are equivalent to [`wait`] except that
-    /// the thread will be blocked for roughly no longer than `dur`. This
-    /// method should not be used for precise timing due to anomalies such as
-    /// preemption or platform differences that may not cause the maximum
-    /// amount of time waited to be precisely `dur`.
-    ///
-    /// Note that the best effort is made to ensure that the time waited is
-    /// measured with a monotonic clock, and not affected by the changes made to
-    /// the system time. This function is susceptible to spurious wakeups.
-    /// Condition variables normally have a boolean predicate associated with
-    /// them, and the predicate must always be checked each time this function
-    /// returns to protect against spurious wakeups. Additionally, it is
-    /// typically desirable for the timeout to not exceed some duration in
-    /// spite of spurious wakes, thus the sleep-duration is decremented by the
-    /// amount slept. Alternatively, use the `wait_timeout_while` method
-    /// to wait with a timeout while a predicate is true.
-    ///
-    /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
-    /// known to have elapsed.
-    ///
-    /// Like [`wait`], the lock specified will be re-acquired when this function
-    /// returns, regardless of whether the timeout elapsed or not.
-    ///
-    /// [`wait`]: #method.wait
-    /// [`wait_timeout_while`]: #method.wait_timeout_while
-    /// [`WaitTimeoutResult`]: struct.WaitTimeoutResult.html
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    /// use std::time::Duration;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut started = lock.lock().unwrap();
-    ///     *started = true;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // wait for the thread to start up
-    /// let (lock, cvar) = &*pair;
-    /// let mut started = lock.lock().unwrap();
-    /// // as long as the value inside the `Mutex<bool>` is `false`, we wait
-    /// loop {
-    ///     let result = cvar.wait_timeout(started, Duration::from_millis(10)).unwrap();
-    ///     // 10 milliseconds have passed, or maybe the value changed!
-    ///     started = result.0;
-    ///     if *started == true {
-    ///         // We received the notification and the value has been updated, we can leave.
-    ///         break
-    ///     }
-    /// }
-    /// ```
-    #[stable(feature = "wait_timeout", since = "1.5.0")]
-    pub fn wait_timeout<'a, T>(
-        &self,
-        guard: MutexGuard<'a, T>,
-        dur: Duration,
-    ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
-        let (poisoned, result) = unsafe {
-            let lock = mutex::guard_lock(&guard);
-            self.verify(lock);
-            let success = self.inner.wait_timeout(lock, dur);
-            (mutex::guard_poison(&guard).get(), WaitTimeoutResult(!success))
-        };
-        if poisoned { Err(PoisonError::new((guard, result))) } else { Ok((guard, result)) }
-    }
-
-    /// Waits on this condition variable for a notification, timing out after a
-    /// specified duration.
-    ///
-    /// The semantics of this function are equivalent to [`wait_while`] except
-    /// that the thread will be blocked for roughly no longer than `dur`. This
-    /// method should not be used for precise timing due to anomalies such as
-    /// preemption or platform differences that may not cause the maximum
-    /// amount of time waited to be precisely `dur`.
-    ///
-    /// Note that the best effort is made to ensure that the time waited is
-    /// measured with a monotonic clock, and not affected by the changes made to
-    /// the system time.
-    ///
-    /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
-    /// known to have elapsed without the condition being met.
-    ///
-    /// Like [`wait_while`], the lock specified will be re-acquired when this
-    /// function returns, regardless of whether the timeout elapsed or not.
-    ///
-    /// [`wait_while`]: #method.wait_while
-    /// [`wait_timeout`]: #method.wait_timeout
-    /// [`WaitTimeoutResult`]: struct.WaitTimeoutResult.html
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    /// use std::time::Duration;
-    ///
-    /// let pair = Arc::new((Mutex::new(true), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut pending = lock.lock().unwrap();
-    ///     *pending = false;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // wait for the thread to start up
-    /// let (lock, cvar) = &*pair;
-    /// let result = cvar.wait_timeout_while(
-    ///     lock.lock().unwrap(),
-    ///     Duration::from_millis(100),
-    ///     |&mut pending| pending,
-    /// ).unwrap();
-    /// if result.1.timed_out() {
-    ///     // timed-out without the condition ever evaluating to false.
-    /// }
-    /// // access the locked mutex via result.0
-    /// ```
-    #[stable(feature = "wait_timeout_until", since = "1.42.0")]
-    pub fn wait_timeout_while<'a, T, F>(
-        &self,
-        mut guard: MutexGuard<'a, T>,
-        dur: Duration,
-        mut condition: F,
-    ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)>
-    where
-        F: FnMut(&mut T) -> bool,
-    {
-        let start = Instant::now();
-        loop {
-            if !condition(&mut *guard) {
-                return Ok((guard, WaitTimeoutResult(false)));
-            }
-            let timeout = match dur.checked_sub(start.elapsed()) {
-                Some(timeout) => timeout,
-                None => return Ok((guard, WaitTimeoutResult(true))),
-            };
-            guard = self.wait_timeout(guard, timeout)?.0;
-        }
-    }
-
-    /// Wakes up one blocked thread on this condvar.
-    ///
-    /// If there is a blocked thread on this condition variable, then it will
-    /// be woken up from its call to [`wait`] or [`wait_timeout`]. Calls to
-    /// `notify_one` are not buffered in any way.
-    ///
-    /// To wake up all threads, see [`notify_all`].
-    ///
-    /// [`wait`]: #method.wait
-    /// [`wait_timeout`]: #method.wait_timeout
-    /// [`notify_all`]: #method.notify_all
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut started = lock.lock().unwrap();
-    ///     *started = true;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_one();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// let mut started = lock.lock().unwrap();
-    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
-    /// while !*started {
-    ///     started = cvar.wait(started).unwrap();
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn notify_one(&self) {
-        unsafe { self.inner.notify_one() }
-    }
-
-    /// Wakes up all blocked threads on this condvar.
-    ///
-    /// This method will ensure that any current waiters on the condition
-    /// variable are awoken. Calls to `notify_all()` are not buffered in any
-    /// way.
-    ///
-    /// To wake up only one thread, see [`notify_one`].
-    ///
-    /// [`notify_one`]: #method.notify_one
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex, Condvar};
-    /// use std::thread;
-    ///
-    /// let pair = Arc::new((Mutex::new(false), Condvar::new()));
-    /// let pair2 = pair.clone();
-    ///
-    /// thread::spawn(move|| {
-    ///     let (lock, cvar) = &*pair2;
-    ///     let mut started = lock.lock().unwrap();
-    ///     *started = true;
-    ///     // We notify the condvar that the value has changed.
-    ///     cvar.notify_all();
-    /// });
-    ///
-    /// // Wait for the thread to start up.
-    /// let (lock, cvar) = &*pair;
-    /// let mut started = lock.lock().unwrap();
-    /// // As long as the value inside the `Mutex<bool>` is `false`, we wait.
-    /// while !*started {
-    ///     started = cvar.wait(started).unwrap();
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn notify_all(&self) {
-        unsafe { self.inner.notify_all() }
-    }
-
-    fn verify(&self, mutex: &sys_mutex::Mutex) {
-        let addr = mutex as *const _ as usize;
-        match self.mutex.compare_and_swap(0, addr, Ordering::SeqCst) {
-            // If we got out 0, then we have successfully bound the mutex to
-            // this cvar.
-            0 => {}
-
-            // If we get out a value that's the same as `addr`, then someone
-            // already beat us to the punch.
-            n if n == addr => {}
-
-            // Anything else and we're using more than one mutex on this cvar,
-            // which is currently disallowed.
-            _ => panic!(
-                "attempted to use a condition variable with two \
-                         mutexes"
-            ),
-        }
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl fmt::Debug for Condvar {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.pad("Condvar { .. }")
-    }
-}
-
-#[stable(feature = "condvar_default", since = "1.10.0")]
-impl Default for Condvar {
-    /// Creates a `Condvar` which is ready to be waited on and notified.
-    fn default() -> Condvar {
-        Condvar::new()
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Drop for Condvar {
-    fn drop(&mut self) {
-        unsafe { self.inner.destroy() }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::sync::atomic::{AtomicBool, Ordering};
-    use crate::sync::mpsc::channel;
-    use crate::sync::{Arc, Condvar, Mutex};
-    use crate::thread;
-    use crate::time::Duration;
-
-    #[test]
-    fn smoke() {
-        let c = Condvar::new();
-        c.notify_one();
-        c.notify_all();
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn notify_one() {
-        let m = Arc::new(Mutex::new(()));
-        let m2 = m.clone();
-        let c = Arc::new(Condvar::new());
-        let c2 = c.clone();
-
-        let g = m.lock().unwrap();
-        let _t = thread::spawn(move || {
-            let _g = m2.lock().unwrap();
-            c2.notify_one();
-        });
-        let g = c.wait(g).unwrap();
-        drop(g);
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn notify_all() {
-        const N: usize = 10;
-
-        let data = Arc::new((Mutex::new(0), Condvar::new()));
-        let (tx, rx) = channel();
-        for _ in 0..N {
-            let data = data.clone();
-            let tx = tx.clone();
-            thread::spawn(move || {
-                let &(ref lock, ref cond) = &*data;
-                let mut cnt = lock.lock().unwrap();
-                *cnt += 1;
-                if *cnt == N {
-                    tx.send(()).unwrap();
-                }
-                while *cnt != 0 {
-                    cnt = cond.wait(cnt).unwrap();
-                }
-                tx.send(()).unwrap();
-            });
-        }
-        drop(tx);
-
-        let &(ref lock, ref cond) = &*data;
-        rx.recv().unwrap();
-        let mut cnt = lock.lock().unwrap();
-        *cnt = 0;
-        cond.notify_all();
-        drop(cnt);
-
-        for _ in 0..N {
-            rx.recv().unwrap();
-        }
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn wait_while() {
-        let pair = Arc::new((Mutex::new(false), Condvar::new()));
-        let pair2 = pair.clone();
-
-        // Inside of our lock, spawn a new thread, and then wait for it to start.
-        thread::spawn(move || {
-            let &(ref lock, ref cvar) = &*pair2;
-            let mut started = lock.lock().unwrap();
-            *started = true;
-            // We notify the condvar that the value has changed.
-            cvar.notify_one();
-        });
-
-        // Wait for the thread to start up.
-        let &(ref lock, ref cvar) = &*pair;
-        let guard = cvar.wait_while(lock.lock().unwrap(), |started| !*started);
-        assert!(*guard.unwrap());
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn wait_timeout_wait() {
-        let m = Arc::new(Mutex::new(()));
-        let c = Arc::new(Condvar::new());
-
-        loop {
-            let g = m.lock().unwrap();
-            let (_g, no_timeout) = c.wait_timeout(g, Duration::from_millis(1)).unwrap();
-            // spurious wakeups mean this isn't necessarily true
-            // so execute test again, if not timeout
-            if !no_timeout.timed_out() {
-                continue;
-            }
-
-            break;
-        }
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn wait_timeout_while_wait() {
-        let m = Arc::new(Mutex::new(()));
-        let c = Arc::new(Condvar::new());
-
-        let g = m.lock().unwrap();
-        let (_g, wait) = c.wait_timeout_while(g, Duration::from_millis(1), |_| true).unwrap();
-        // no spurious wakeups. ensure it timed-out
-        assert!(wait.timed_out());
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn wait_timeout_while_instant_satisfy() {
-        let m = Arc::new(Mutex::new(()));
-        let c = Arc::new(Condvar::new());
-
-        let g = m.lock().unwrap();
-        let (_g, wait) = c.wait_timeout_while(g, Duration::from_millis(0), |_| false).unwrap();
-        // ensure it didn't time-out even if we were not given any time.
-        assert!(!wait.timed_out());
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn wait_timeout_while_wake() {
-        let pair = Arc::new((Mutex::new(false), Condvar::new()));
-        let pair_copy = pair.clone();
-
-        let &(ref m, ref c) = &*pair;
-        let g = m.lock().unwrap();
-        let _t = thread::spawn(move || {
-            let &(ref lock, ref cvar) = &*pair_copy;
-            let mut started = lock.lock().unwrap();
-            thread::sleep(Duration::from_millis(1));
-            *started = true;
-            cvar.notify_one();
-        });
-        let (g2, wait) = c
-            .wait_timeout_while(g, Duration::from_millis(u64::MAX), |&mut notified| !notified)
-            .unwrap();
-        // ensure it didn't time-out even if we were not given any time.
-        assert!(!wait.timed_out());
-        assert!(*g2);
-    }
-
-    #[test]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn wait_timeout_wake() {
-        let m = Arc::new(Mutex::new(()));
-        let c = Arc::new(Condvar::new());
-
-        loop {
-            let g = m.lock().unwrap();
-
-            let c2 = c.clone();
-            let m2 = m.clone();
-
-            let notified = Arc::new(AtomicBool::new(false));
-            let notified_copy = notified.clone();
-
-            let t = thread::spawn(move || {
-                let _g = m2.lock().unwrap();
-                thread::sleep(Duration::from_millis(1));
-                notified_copy.store(true, Ordering::SeqCst);
-                c2.notify_one();
-            });
-            let (g, timeout_res) = c.wait_timeout(g, Duration::from_millis(u64::MAX)).unwrap();
-            assert!(!timeout_res.timed_out());
-            // spurious wakeups mean this isn't necessarily true
-            // so execute test again, if not notified
-            if !notified.load(Ordering::SeqCst) {
-                t.join().unwrap();
-                continue;
-            }
-            drop(g);
-
-            t.join().unwrap();
-
-            break;
-        }
-    }
-
-    #[test]
-    #[should_panic]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn two_mutexes() {
-        let m = Arc::new(Mutex::new(()));
-        let m2 = m.clone();
-        let c = Arc::new(Condvar::new());
-        let c2 = c.clone();
-
-        let mut g = m.lock().unwrap();
-        let _t = thread::spawn(move || {
-            let _g = m2.lock().unwrap();
-            c2.notify_one();
-        });
-        g = c.wait(g).unwrap();
-        drop(g);
-
-        let m = Mutex::new(());
-        let _ = c.wait(m.lock().unwrap()).unwrap();
-    }
-}
diff --git a/src/libstd/sync/mod.rs b/src/libstd/sync/mod.rs
deleted file mode 100644
index b6699910b07..00000000000
--- a/src/libstd/sync/mod.rs
+++ /dev/null
@@ -1,179 +0,0 @@
-//! Useful synchronization primitives.
-//!
-//! ## The need for synchronization
-//!
-//! Conceptually, a Rust program is a series of operations which will
-//! be executed on a computer. The timeline of events happening in the
-//! program is consistent with the order of the operations in the code.
-//!
-//! Consider the following code, operating on some global static variables:
-//!
-//! ```rust
-//! static mut A: u32 = 0;
-//! static mut B: u32 = 0;
-//! static mut C: u32 = 0;
-//!
-//! fn main() {
-//!     unsafe {
-//!         A = 3;
-//!         B = 4;
-//!         A = A + B;
-//!         C = B;
-//!         println!("{} {} {}", A, B, C);
-//!         C = A;
-//!     }
-//! }
-//! ```
-//!
-//! It appears as if some variables stored in memory are changed, an addition
-//! is performed, result is stored in `A` and the variable `C` is
-//! modified twice.
-//!
-//! When only a single thread is involved, the results are as expected:
-//! the line `7 4 4` gets printed.
-//!
-//! As for what happens behind the scenes, when optimizations are enabled the
-//! final generated machine code might look very different from the code:
-//!
-//! - The first store to `C` might be moved before the store to `A` or `B`,
-//!   _as if_ we had written `C = 4; A = 3; B = 4`.
-//!
-//! - Assignment of `A + B` to `A` might be removed, since the sum can be stored
-//!   in a temporary location until it gets printed, with the global variable
-//!   never getting updated.
-//!
-//! - The final result could be determined just by looking at the code
-//!   at compile time, so [constant folding] might turn the whole
-//!   block into a simple `println!("7 4 4")`.
-//!
-//! The compiler is allowed to perform any combination of these
-//! optimizations, as long as the final optimized code, when executed,
-//! produces the same results as the one without optimizations.
-//!
-//! Due to the [concurrency] involved in modern computers, assumptions
-//! about the program's execution order are often wrong. Access to
-//! global variables can lead to nondeterministic results, **even if**
-//! compiler optimizations are disabled, and it is **still possible**
-//! to introduce synchronization bugs.
-//!
-//! Note that thanks to Rust's safety guarantees, accessing global (static)
-//! variables requires `unsafe` code, assuming we don't use any of the
-//! synchronization primitives in this module.
-//!
-//! [constant folding]: https://en.wikipedia.org/wiki/Constant_folding
-//! [concurrency]: https://en.wikipedia.org/wiki/Concurrency_(computer_science)
-//!
-//! ## Out-of-order execution
-//!
-//! Instructions can execute in a different order from the one we define, due to
-//! various reasons:
-//!
-//! - The **compiler** reordering instructions: If the compiler can issue an
-//!   instruction at an earlier point, it will try to do so. For example, it
-//!   might hoist memory loads at the top of a code block, so that the CPU can
-//!   start [prefetching] the values from memory.
-//!
-//!   In single-threaded scenarios, this can cause issues when writing
-//!   signal handlers or certain kinds of low-level code.
-//!   Use [compiler fences] to prevent this reordering.
-//!
-//! - A **single processor** executing instructions [out-of-order]:
-//!   Modern CPUs are capable of [superscalar] execution,
-//!   i.e., multiple instructions might be executing at the same time,
-//!   even though the machine code describes a sequential process.
-//!
-//!   This kind of reordering is handled transparently by the CPU.
-//!
-//! - A **multiprocessor** system executing multiple hardware threads
-//!   at the same time: In multi-threaded scenarios, you can use two
-//!   kinds of primitives to deal with synchronization:
-//!   - [memory fences] to ensure memory accesses are made visible to
-//!   other CPUs in the right order.
-//!   - [atomic operations] to ensure simultaneous access to the same
-//!   memory location doesn't lead to undefined behavior.
-//!
-//! [prefetching]: https://en.wikipedia.org/wiki/Cache_prefetching
-//! [compiler fences]: crate::sync::atomic::compiler_fence
-//! [out-of-order]: https://en.wikipedia.org/wiki/Out-of-order_execution
-//! [superscalar]: https://en.wikipedia.org/wiki/Superscalar_processor
-//! [memory fences]: crate::sync::atomic::fence
-//! [atomic operations]: crate::sync::atomic
-//!
-//! ## Higher-level synchronization objects
-//!
-//! Most of the low-level synchronization primitives are quite error-prone and
-//! inconvenient to use, which is why the standard library also exposes some
-//! higher-level synchronization objects.
-//!
-//! These abstractions can be built out of lower-level primitives.
-//! For efficiency, the sync objects in the standard library are usually
-//! implemented with help from the operating system's kernel, which is
-//! able to reschedule the threads while they are blocked on acquiring
-//! a lock.
-//!
-//! The following is an overview of the available synchronization
-//! objects:
-//!
-//! - [`Arc`]: Atomically Reference-Counted pointer, which can be used
-//!   in multithreaded environments to prolong the lifetime of some
-//!   data until all the threads have finished using it.
-//!
-//! - [`Barrier`]: Ensures multiple threads will wait for each other
-//!   to reach a point in the program, before continuing execution all
-//!   together.
-//!
-//! - [`Condvar`]: Condition Variable, providing the ability to block
-//!   a thread while waiting for an event to occur.
-//!
-//! - [`mpsc`]: Multi-producer, single-consumer queues, used for
-//!   message-based communication. Can provide a lightweight
-//!   inter-thread synchronisation mechanism, at the cost of some
-//!   extra memory.
-//!
-//! - [`Mutex`]: Mutual Exclusion mechanism, which ensures that at
-//!   most one thread at a time is able to access some data.
-//!
-//! - [`Once`]: Used for thread-safe, one-time initialization of a
-//!   global variable.
-//!
-//! - [`RwLock`]: Provides a mutual exclusion mechanism which allows
-//!   multiple readers at the same time, while allowing only one
-//!   writer at a time. In some cases, this can be more efficient than
-//!   a mutex.
-//!
-//! [`Arc`]: crate::sync::Arc
-//! [`Barrier`]: crate::sync::Barrier
-//! [`Condvar`]: crate::sync::Condvar
-//! [`mpsc`]: crate::sync::mpsc
-//! [`Mutex`]: crate::sync::Mutex
-//! [`Once`]: crate::sync::Once
-//! [`RwLock`]: crate::sync::RwLock
-
-#![stable(feature = "rust1", since = "1.0.0")]
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use alloc_crate::sync::{Arc, Weak};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use core::sync::atomic;
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::barrier::{Barrier, BarrierWaitResult};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::condvar::{Condvar, WaitTimeoutResult};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::mutex::{Mutex, MutexGuard};
-#[stable(feature = "rust1", since = "1.0.0")]
-#[allow(deprecated)]
-pub use self::once::{Once, OnceState, ONCE_INIT};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use self::rwlock::{RwLock, RwLockReadGuard, RwLockWriteGuard};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use crate::sys_common::poison::{LockResult, PoisonError, TryLockError, TryLockResult};
-
-pub mod mpsc;
-
-mod barrier;
-mod condvar;
-mod mutex;
-mod once;
-mod rwlock;
diff --git a/src/libstd/sync/mpsc/blocking.rs b/src/libstd/sync/mpsc/blocking.rs
deleted file mode 100644
index d34de6a4fac..00000000000
--- a/src/libstd/sync/mpsc/blocking.rs
+++ /dev/null
@@ -1,79 +0,0 @@
-//! Generic support for building blocking abstractions.
-
-use crate::mem;
-use crate::sync::atomic::{AtomicBool, Ordering};
-use crate::sync::Arc;
-use crate::thread::{self, Thread};
-use crate::time::Instant;
-
-struct Inner {
-    thread: Thread,
-    woken: AtomicBool,
-}
-
-unsafe impl Send for Inner {}
-unsafe impl Sync for Inner {}
-
-#[derive(Clone)]
-pub struct SignalToken {
-    inner: Arc<Inner>,
-}
-
-pub struct WaitToken {
-    inner: Arc<Inner>,
-}
-
-impl !Send for WaitToken {}
-
-impl !Sync for WaitToken {}
-
-pub fn tokens() -> (WaitToken, SignalToken) {
-    let inner = Arc::new(Inner { thread: thread::current(), woken: AtomicBool::new(false) });
-    let wait_token = WaitToken { inner: inner.clone() };
-    let signal_token = SignalToken { inner };
-    (wait_token, signal_token)
-}
-
-impl SignalToken {
-    pub fn signal(&self) -> bool {
-        let wake = !self.inner.woken.compare_and_swap(false, true, Ordering::SeqCst);
-        if wake {
-            self.inner.thread.unpark();
-        }
-        wake
-    }
-
-    /// Converts to an unsafe usize value. Useful for storing in a pipe's state
-    /// flag.
-    #[inline]
-    pub unsafe fn cast_to_usize(self) -> usize {
-        mem::transmute(self.inner)
-    }
-
-    /// Converts from an unsafe usize value. Useful for retrieving a pipe's state
-    /// flag.
-    #[inline]
-    pub unsafe fn cast_from_usize(signal_ptr: usize) -> SignalToken {
-        SignalToken { inner: mem::transmute(signal_ptr) }
-    }
-}
-
-impl WaitToken {
-    pub fn wait(self) {
-        while !self.inner.woken.load(Ordering::SeqCst) {
-            thread::park()
-        }
-    }
-
-    /// Returns `true` if we wake up normally.
-    pub fn wait_max_until(self, end: Instant) -> bool {
-        while !self.inner.woken.load(Ordering::SeqCst) {
-            let now = Instant::now();
-            if now >= end {
-                return false;
-            }
-            thread::park_timeout(end - now)
-        }
-        true
-    }
-}
diff --git a/src/libstd/sync/mpsc/cache_aligned.rs b/src/libstd/sync/mpsc/cache_aligned.rs
deleted file mode 100644
index b0842144328..00000000000
--- a/src/libstd/sync/mpsc/cache_aligned.rs
+++ /dev/null
@@ -1,27 +0,0 @@
-use crate::ops::{Deref, DerefMut};
-
-#[derive(Copy, Clone, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[repr(align(64))]
-pub(super) struct Aligner;
-
-#[derive(Copy, Clone, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub(super) struct CacheAligned<T>(pub T, pub Aligner);
-
-impl<T> Deref for CacheAligned<T> {
-    type Target = T;
-    fn deref(&self) -> &Self::Target {
-        &self.0
-    }
-}
-
-impl<T> DerefMut for CacheAligned<T> {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.0
-    }
-}
-
-impl<T> CacheAligned<T> {
-    pub(super) fn new(t: T) -> Self {
-        CacheAligned(t, Aligner)
-    }
-}
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
deleted file mode 100644
index 3ff50e9f213..00000000000
--- a/src/libstd/sync/mpsc/mod.rs
+++ /dev/null
@@ -1,3033 +0,0 @@
-// ignore-tidy-filelength
-
-//! Multi-producer, single-consumer FIFO queue communication primitives.
-//!
-//! This module provides message-based communication over channels, concretely
-//! defined among three types:
-//!
-//! * [`Sender`]
-//! * [`SyncSender`]
-//! * [`Receiver`]
-//!
-//! A [`Sender`] or [`SyncSender`] is used to send data to a [`Receiver`]. Both
-//! senders are clone-able (multi-producer) such that many threads can send
-//! simultaneously to one receiver (single-consumer).
-//!
-//! These channels come in two flavors:
-//!
-//! 1. An asynchronous, infinitely buffered channel. The [`channel`] function
-//!    will return a `(Sender, Receiver)` tuple where all sends will be
-//!    **asynchronous** (they never block). The channel conceptually has an
-//!    infinite buffer.
-//!
-//! 2. A synchronous, bounded channel. The [`sync_channel`] function will
-//!    return a `(SyncSender, Receiver)` tuple where the storage for pending
-//!    messages is a pre-allocated buffer of a fixed size. All sends will be
-//!    **synchronous** by blocking until there is buffer space available. Note
-//!    that a bound of 0 is allowed, causing the channel to become a "rendezvous"
-//!    channel where each sender atomically hands off a message to a receiver.
-//!
-//! [`Sender`]: ../../../std/sync/mpsc/struct.Sender.html
-//! [`SyncSender`]: ../../../std/sync/mpsc/struct.SyncSender.html
-//! [`Receiver`]: ../../../std/sync/mpsc/struct.Receiver.html
-//! [`send`]: ../../../std/sync/mpsc/struct.Sender.html#method.send
-//! [`channel`]: ../../../std/sync/mpsc/fn.channel.html
-//! [`sync_channel`]: ../../../std/sync/mpsc/fn.sync_channel.html
-//!
-//! ## Disconnection
-//!
-//! The send and receive operations on channels will all return a [`Result`]
-//! indicating whether the operation succeeded or not. An unsuccessful operation
-//! is normally indicative of the other half of a channel having "hung up" by
-//! being dropped in its corresponding thread.
-//!
-//! Once half of a channel has been deallocated, most operations can no longer
-//! continue to make progress, so [`Err`] will be returned. Many applications
-//! will continue to [`unwrap`] the results returned from this module,
-//! instigating a propagation of failure among threads if one unexpectedly dies.
-//!
-//! [`Result`]: ../../../std/result/enum.Result.html
-//! [`Err`]: ../../../std/result/enum.Result.html#variant.Err
-//! [`unwrap`]: ../../../std/result/enum.Result.html#method.unwrap
-//!
-//! # Examples
-//!
-//! Simple usage:
-//!
-//! ```
-//! use std::thread;
-//! use std::sync::mpsc::channel;
-//!
-//! // Create a simple streaming channel
-//! let (tx, rx) = channel();
-//! thread::spawn(move|| {
-//!     tx.send(10).unwrap();
-//! });
-//! assert_eq!(rx.recv().unwrap(), 10);
-//! ```
-//!
-//! Shared usage:
-//!
-//! ```
-//! use std::thread;
-//! use std::sync::mpsc::channel;
-//!
-//! // Create a shared channel that can be sent along from many threads
-//! // where tx is the sending half (tx for transmission), and rx is the receiving
-//! // half (rx for receiving).
-//! let (tx, rx) = channel();
-//! for i in 0..10 {
-//!     let tx = tx.clone();
-//!     thread::spawn(move|| {
-//!         tx.send(i).unwrap();
-//!     });
-//! }
-//!
-//! for _ in 0..10 {
-//!     let j = rx.recv().unwrap();
-//!     assert!(0 <= j && j < 10);
-//! }
-//! ```
-//!
-//! Propagating panics:
-//!
-//! ```
-//! use std::sync::mpsc::channel;
-//!
-//! // The call to recv() will return an error because the channel has already
-//! // hung up (or been deallocated)
-//! let (tx, rx) = channel::<i32>();
-//! drop(tx);
-//! assert!(rx.recv().is_err());
-//! ```
-//!
-//! Synchronous channels:
-//!
-//! ```
-//! use std::thread;
-//! use std::sync::mpsc::sync_channel;
-//!
-//! let (tx, rx) = sync_channel::<i32>(0);
-//! thread::spawn(move|| {
-//!     // This will wait for the parent thread to start receiving
-//!     tx.send(53).unwrap();
-//! });
-//! rx.recv().unwrap();
-//! ```
-
-#![stable(feature = "rust1", since = "1.0.0")]
-
-// A description of how Rust's channel implementation works
-//
-// Channels are supposed to be the basic building block for all other
-// concurrent primitives that are used in Rust. As a result, the channel type
-// needs to be highly optimized, flexible, and broad enough for use everywhere.
-//
-// The choice of implementation of all channels is to be built on lock-free data
-// structures. The channels themselves are then consequently also lock-free data
-// structures. As always with lock-free code, this is a very "here be dragons"
-// territory, especially because I'm unaware of any academic papers that have
-// gone into great length about channels of these flavors.
-//
-// ## Flavors of channels
-//
-// From the perspective of a consumer of this library, there is only one flavor
-// of channel. This channel can be used as a stream and cloned to allow multiple
-// senders. Under the hood, however, there are actually three flavors of
-// channels in play.
-//
-// * Flavor::Oneshots - these channels are highly optimized for the one-send use
-//                      case. They contain as few atomics as possible and
-//                      involve one and exactly one allocation.
-// * Streams - these channels are optimized for the non-shared use case. They
-//             use a different concurrent queue that is more tailored for this
-//             use case. The initial allocation of this flavor of channel is not
-//             optimized.
-// * Shared - this is the most general form of channel that this module offers,
-//            a channel with multiple senders. This type is as optimized as it
-//            can be, but the previous two types mentioned are much faster for
-//            their use-cases.
-//
-// ## Concurrent queues
-//
-// The basic idea of Rust's Sender/Receiver types is that send() never blocks,
-// but recv() obviously blocks. This means that under the hood there must be
-// some shared and concurrent queue holding all of the actual data.
-//
-// With two flavors of channels, two flavors of queues are also used. We have
-// chosen to use queues from a well-known author that are abbreviated as SPSC
-// and MPSC (single producer, single consumer and multiple producer, single
-// consumer). SPSC queues are used for streams while MPSC queues are used for
-// shared channels.
-//
-// ### SPSC optimizations
-//
-// The SPSC queue found online is essentially a linked list of nodes where one
-// half of the nodes are the "queue of data" and the other half of nodes are a
-// cache of unused nodes. The unused nodes are used such that an allocation is
-// not required on every push() and a free doesn't need to happen on every
-// pop().
-//
-// As found online, however, the cache of nodes is of an infinite size. This
-// means that if a channel at one point in its life had 50k items in the queue,
-// then the queue will always have the capacity for 50k items. I believed that
-// this was an unnecessary limitation of the implementation, so I have altered
-// the queue to optionally have a bound on the cache size.
-//
-// By default, streams will have an unbounded SPSC queue with a small-ish cache
-// size. The hope is that the cache is still large enough to have very fast
-// send() operations while not too large such that millions of channels can
-// coexist at once.
-//
-// ### MPSC optimizations
-//
-// Right now the MPSC queue has not been optimized. Like the SPSC queue, it uses
-// a linked list under the hood to earn its unboundedness, but I have not put
-// forth much effort into having a cache of nodes similar to the SPSC queue.
-//
-// For now, I believe that this is "ok" because shared channels are not the most
-// common type, but soon we may wish to revisit this queue choice and determine
-// another candidate for backend storage of shared channels.
-//
-// ## Overview of the Implementation
-//
-// Now that there's a little background on the concurrent queues used, it's
-// worth going into much more detail about the channels themselves. The basic
-// pseudocode for a send/recv are:
-//
-//
-//      send(t)                             recv()
-//        queue.push(t)                       return if queue.pop()
-//        if increment() == -1                deschedule {
-//          wakeup()                            if decrement() > 0
-//                                                cancel_deschedule()
-//                                            }
-//                                            queue.pop()
-//
-// As mentioned before, there are no locks in this implementation, only atomic
-// instructions are used.
-//
-// ### The internal atomic counter
-//
-// Every channel has a shared counter with each half to keep track of the size
-// of the queue. This counter is used to abort descheduling by the receiver and
-// to know when to wake up on the sending side.
-//
-// As seen in the pseudocode, senders will increment this count and receivers
-// will decrement the count. The theory behind this is that if a sender sees a
-// -1 count, it will wake up the receiver, and if the receiver sees a 1+ count,
-// then it doesn't need to block.
-//
-// The recv() method has a beginning call to pop(), and if successful, it needs
-// to decrement the count. It is a crucial implementation detail that this
-// decrement does *not* happen to the shared counter. If this were the case,
-// then it would be possible for the counter to be very negative when there were
-// no receivers waiting, in which case the senders would have to determine when
-// it was actually appropriate to wake up a receiver.
-//
-// Instead, the "steal count" is kept track of separately (not atomically
-// because it's only used by receivers), and then the decrement() call when
-// descheduling will lump in all of the recent steals into one large decrement.
-//
-// The implication of this is that if a sender sees a -1 count, then there's
-// guaranteed to be a waiter waiting!
-//
-// ## Native Implementation
-//
-// A major goal of these channels is to work seamlessly on and off the runtime.
-// All of the previous race conditions have been worded in terms of
-// scheduler-isms (which is obviously not available without the runtime).
-//
-// For now, native usage of channels (off the runtime) will fall back onto
-// mutexes/cond vars for descheduling/atomic decisions. The no-contention path
-// is still entirely lock-free, the "deschedule" blocks above are surrounded by
-// a mutex and the "wakeup" blocks involve grabbing a mutex and signaling on a
-// condition variable.
-//
-// ## Select
-//
-// Being able to support selection over channels has greatly influenced this
-// design, and not only does selection need to work inside the runtime, but also
-// outside the runtime.
-//
-// The implementation is fairly straightforward. The goal of select() is not to
-// return some data, but only to return which channel can receive data without
-// blocking. The implementation is essentially the entire blocking procedure
-// followed by an increment as soon as its woken up. The cancellation procedure
-// involves an increment and swapping out of to_wake to acquire ownership of the
-// thread to unblock.
-//
-// Sadly this current implementation requires multiple allocations, so I have
-// seen the throughput of select() be much worse than it should be. I do not
-// believe that there is anything fundamental that needs to change about these
-// channels, however, in order to support a more efficient select().
-//
-// FIXME: Select is now removed, so these factors are ready to be cleaned up!
-//
-// # Conclusion
-//
-// And now that you've seen all the races that I found and attempted to fix,
-// here's the code for you to find some more!
-
-use crate::cell::UnsafeCell;
-use crate::error;
-use crate::fmt;
-use crate::mem;
-use crate::sync::Arc;
-use crate::time::{Duration, Instant};
-
-mod blocking;
-mod mpsc_queue;
-mod oneshot;
-mod shared;
-mod spsc_queue;
-mod stream;
-mod sync;
-
-mod cache_aligned;
-
-/// The receiving half of Rust's [`channel`] (or [`sync_channel`]) type.
-/// This half can only be owned by one thread.
-///
-/// Messages sent to the channel can be retrieved using [`recv`].
-///
-/// [`channel`]: fn.channel.html
-/// [`sync_channel`]: fn.sync_channel.html
-/// [`recv`]: struct.Receiver.html#method.recv
-///
-/// # Examples
-///
-/// ```rust
-/// use std::sync::mpsc::channel;
-/// use std::thread;
-/// use std::time::Duration;
-///
-/// let (send, recv) = channel();
-///
-/// thread::spawn(move || {
-///     send.send("Hello world!").unwrap();
-///     thread::sleep(Duration::from_secs(2)); // block for two seconds
-///     send.send("Delayed for 2 seconds").unwrap();
-/// });
-///
-/// println!("{}", recv.recv().unwrap()); // Received immediately
-/// println!("Waiting...");
-/// println!("{}", recv.recv().unwrap()); // Received after 2 seconds
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Receiver<T> {
-    inner: UnsafeCell<Flavor<T>>,
-}
-
-// The receiver port can be sent from place to place, so long as it
-// is not used to receive non-sendable things.
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: Send> Send for Receiver<T> {}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> !Sync for Receiver<T> {}
-
-/// An iterator over messages on a [`Receiver`], created by [`iter`].
-///
-/// This iterator will block whenever [`next`] is called,
-/// waiting for a new message, and [`None`] will be returned
-/// when the corresponding channel has hung up.
-///
-/// [`iter`]: struct.Receiver.html#method.iter
-/// [`Receiver`]: struct.Receiver.html
-/// [`next`]: ../../../std/iter/trait.Iterator.html#tymethod.next
-/// [`None`]: ../../../std/option/enum.Option.html#variant.None
-///
-/// # Examples
-///
-/// ```rust
-/// use std::sync::mpsc::channel;
-/// use std::thread;
-///
-/// let (send, recv) = channel();
-///
-/// thread::spawn(move || {
-///     send.send(1u8).unwrap();
-///     send.send(2u8).unwrap();
-///     send.send(3u8).unwrap();
-/// });
-///
-/// for x in recv.iter() {
-///     println!("Got: {}", x);
-/// }
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Debug)]
-pub struct Iter<'a, T: 'a> {
-    rx: &'a Receiver<T>,
-}
-
-/// An iterator that attempts to yield all pending values for a [`Receiver`],
-/// created by [`try_iter`].
-///
-/// [`None`] will be returned when there are no pending values remaining or
-/// if the corresponding channel has hung up.
-///
-/// This iterator will never block the caller in order to wait for data to
-/// become available. Instead, it will return [`None`].
-///
-/// [`Receiver`]: struct.Receiver.html
-/// [`try_iter`]: struct.Receiver.html#method.try_iter
-/// [`None`]: ../../../std/option/enum.Option.html#variant.None
-///
-/// # Examples
-///
-/// ```rust
-/// use std::sync::mpsc::channel;
-/// use std::thread;
-/// use std::time::Duration;
-///
-/// let (sender, receiver) = channel();
-///
-/// // Nothing is in the buffer yet
-/// assert!(receiver.try_iter().next().is_none());
-/// println!("Nothing in the buffer...");
-///
-/// thread::spawn(move || {
-///     sender.send(1).unwrap();
-///     sender.send(2).unwrap();
-///     sender.send(3).unwrap();
-/// });
-///
-/// println!("Going to sleep...");
-/// thread::sleep(Duration::from_secs(2)); // block for two seconds
-///
-/// for x in receiver.try_iter() {
-///     println!("Got: {}", x);
-/// }
-/// ```
-#[stable(feature = "receiver_try_iter", since = "1.15.0")]
-#[derive(Debug)]
-pub struct TryIter<'a, T: 'a> {
-    rx: &'a Receiver<T>,
-}
-
-/// An owning iterator over messages on a [`Receiver`],
-/// created by **Receiver::into_iter**.
-///
-/// This iterator will block whenever [`next`]
-/// is called, waiting for a new message, and [`None`] will be
-/// returned if the corresponding channel has hung up.
-///
-/// [`Receiver`]: struct.Receiver.html
-/// [`next`]: ../../../std/iter/trait.Iterator.html#tymethod.next
-/// [`None`]: ../../../std/option/enum.Option.html#variant.None
-///
-/// # Examples
-///
-/// ```rust
-/// use std::sync::mpsc::channel;
-/// use std::thread;
-///
-/// let (send, recv) = channel();
-///
-/// thread::spawn(move || {
-///     send.send(1u8).unwrap();
-///     send.send(2u8).unwrap();
-///     send.send(3u8).unwrap();
-/// });
-///
-/// for x in recv.into_iter() {
-///     println!("Got: {}", x);
-/// }
-/// ```
-#[stable(feature = "receiver_into_iter", since = "1.1.0")]
-#[derive(Debug)]
-pub struct IntoIter<T> {
-    rx: Receiver<T>,
-}
-
-/// The sending-half of Rust's asynchronous [`channel`] type. This half can only be
-/// owned by one thread, but it can be cloned to send to other threads.
-///
-/// Messages can be sent through this channel with [`send`].
-///
-/// [`channel`]: fn.channel.html
-/// [`send`]: struct.Sender.html#method.send
-///
-/// # Examples
-///
-/// ```rust
-/// use std::sync::mpsc::channel;
-/// use std::thread;
-///
-/// let (sender, receiver) = channel();
-/// let sender2 = sender.clone();
-///
-/// // First thread owns sender
-/// thread::spawn(move || {
-///     sender.send(1).unwrap();
-/// });
-///
-/// // Second thread owns sender2
-/// thread::spawn(move || {
-///     sender2.send(2).unwrap();
-/// });
-///
-/// let msg = receiver.recv().unwrap();
-/// let msg2 = receiver.recv().unwrap();
-///
-/// assert_eq!(3, msg + msg2);
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Sender<T> {
-    inner: UnsafeCell<Flavor<T>>,
-}
-
-// The send port can be sent from place to place, so long as it
-// is not used to send non-sendable things.
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: Send> Send for Sender<T> {}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> !Sync for Sender<T> {}
-
-/// The sending-half of Rust's synchronous [`sync_channel`] type.
-///
-/// Messages can be sent through this channel with [`send`] or [`try_send`].
-///
-/// [`send`] will block if there is no space in the internal buffer.
-///
-/// [`sync_channel`]: fn.sync_channel.html
-/// [`send`]: struct.SyncSender.html#method.send
-/// [`try_send`]: struct.SyncSender.html#method.try_send
-///
-/// # Examples
-///
-/// ```rust
-/// use std::sync::mpsc::sync_channel;
-/// use std::thread;
-///
-/// // Create a sync_channel with buffer size 2
-/// let (sync_sender, receiver) = sync_channel(2);
-/// let sync_sender2 = sync_sender.clone();
-///
-/// // First thread owns sync_sender
-/// thread::spawn(move || {
-///     sync_sender.send(1).unwrap();
-///     sync_sender.send(2).unwrap();
-/// });
-///
-/// // Second thread owns sync_sender2
-/// thread::spawn(move || {
-///     sync_sender2.send(3).unwrap();
-///     // thread will now block since the buffer is full
-///     println!("Thread unblocked!");
-/// });
-///
-/// let mut msg;
-///
-/// msg = receiver.recv().unwrap();
-/// println!("message {} received", msg);
-///
-/// // "Thread unblocked!" will be printed now
-///
-/// msg = receiver.recv().unwrap();
-/// println!("message {} received", msg);
-///
-/// msg = receiver.recv().unwrap();
-///
-/// println!("message {} received", msg);
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct SyncSender<T> {
-    inner: Arc<sync::Packet<T>>,
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: Send> Send for SyncSender<T> {}
-
-/// An error returned from the [`Sender::send`] or [`SyncSender::send`]
-/// function on **channel**s.
-///
-/// A **send** operation can only fail if the receiving end of a channel is
-/// disconnected, implying that the data could never be received. The error
-/// contains the data being sent as a payload so it can be recovered.
-///
-/// [`Sender::send`]: struct.Sender.html#method.send
-/// [`SyncSender::send`]: struct.SyncSender.html#method.send
-#[stable(feature = "rust1", since = "1.0.0")]
-#[derive(PartialEq, Eq, Clone, Copy)]
-pub struct SendError<T>(#[stable(feature = "rust1", since = "1.0.0")] pub T);
-
-/// An error returned from the [`recv`] function on a [`Receiver`].
-///
-/// The [`recv`] operation can only fail if the sending half of a
-/// [`channel`] (or [`sync_channel`]) is disconnected, implying that no further
-/// messages will ever be received.
-///
-/// [`recv`]: struct.Receiver.html#method.recv
-/// [`Receiver`]: struct.Receiver.html
-/// [`channel`]: fn.channel.html
-/// [`sync_channel`]: fn.sync_channel.html
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct RecvError;
-
-/// This enumeration is the list of the possible reasons that [`try_recv`] could
-/// not return data when called. This can occur with both a [`channel`] and
-/// a [`sync_channel`].
-///
-/// [`try_recv`]: struct.Receiver.html#method.try_recv
-/// [`channel`]: fn.channel.html
-/// [`sync_channel`]: fn.sync_channel.html
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub enum TryRecvError {
-    /// This **channel** is currently empty, but the **Sender**(s) have not yet
-    /// disconnected, so data may yet become available.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Empty,
-
-    /// The **channel**'s sending half has become disconnected, and there will
-    /// never be any more data received on it.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Disconnected,
-}
-
-/// This enumeration is the list of possible errors that made [`recv_timeout`]
-/// unable to return data when called. This can occur with both a [`channel`] and
-/// a [`sync_channel`].
-///
-/// [`recv_timeout`]: struct.Receiver.html#method.recv_timeout
-/// [`channel`]: fn.channel.html
-/// [`sync_channel`]: fn.sync_channel.html
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
-#[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
-pub enum RecvTimeoutError {
-    /// This **channel** is currently empty, but the **Sender**(s) have not yet
-    /// disconnected, so data may yet become available.
-    #[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
-    Timeout,
-    /// The **channel**'s sending half has become disconnected, and there will
-    /// never be any more data received on it.
-    #[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
-    Disconnected,
-}
-
-/// This enumeration is the list of the possible error outcomes for the
-/// [`try_send`] method.
-///
-/// [`try_send`]: struct.SyncSender.html#method.try_send
-#[stable(feature = "rust1", since = "1.0.0")]
-#[derive(PartialEq, Eq, Clone, Copy)]
-pub enum TrySendError<T> {
-    /// The data could not be sent on the [`sync_channel`] because it would require that
-    /// the callee block to send the data.
-    ///
-    /// If this is a buffered channel, then the buffer is full at this time. If
-    /// this is not a buffered channel, then there is no [`Receiver`] available to
-    /// acquire the data.
-    ///
-    /// [`sync_channel`]: fn.sync_channel.html
-    /// [`Receiver`]: struct.Receiver.html
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Full(#[stable(feature = "rust1", since = "1.0.0")] T),
-
-    /// This [`sync_channel`]'s receiving half has disconnected, so the data could not be
-    /// sent. The data is returned back to the callee in this case.
-    ///
-    /// [`sync_channel`]: fn.sync_channel.html
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Disconnected(#[stable(feature = "rust1", since = "1.0.0")] T),
-}
-
-enum Flavor<T> {
-    Oneshot(Arc<oneshot::Packet<T>>),
-    Stream(Arc<stream::Packet<T>>),
-    Shared(Arc<shared::Packet<T>>),
-    Sync(Arc<sync::Packet<T>>),
-}
-
-#[doc(hidden)]
-trait UnsafeFlavor<T> {
-    fn inner_unsafe(&self) -> &UnsafeCell<Flavor<T>>;
-    unsafe fn inner_mut(&self) -> &mut Flavor<T> {
-        &mut *self.inner_unsafe().get()
-    }
-    unsafe fn inner(&self) -> &Flavor<T> {
-        &*self.inner_unsafe().get()
-    }
-}
-impl<T> UnsafeFlavor<T> for Sender<T> {
-    fn inner_unsafe(&self) -> &UnsafeCell<Flavor<T>> {
-        &self.inner
-    }
-}
-impl<T> UnsafeFlavor<T> for Receiver<T> {
-    fn inner_unsafe(&self) -> &UnsafeCell<Flavor<T>> {
-        &self.inner
-    }
-}
-
-/// Creates a new asynchronous channel, returning the sender/receiver halves.
-/// All data sent on the [`Sender`] will become available on the [`Receiver`] in
-/// the same order as it was sent, and no [`send`] will block the calling thread
-/// (this channel has an "infinite buffer", unlike [`sync_channel`], which will
-/// block after its buffer limit is reached). [`recv`] will block until a message
-/// is available.
-///
-/// The [`Sender`] can be cloned to [`send`] to the same channel multiple times, but
-/// only one [`Receiver`] is supported.
-///
-/// If the [`Receiver`] is disconnected while trying to [`send`] with the
-/// [`Sender`], the [`send`] method will return a [`SendError`]. Similarly, if the
-/// [`Sender`] is disconnected while trying to [`recv`], the [`recv`] method will
-/// return a [`RecvError`].
-///
-/// [`send`]: struct.Sender.html#method.send
-/// [`recv`]: struct.Receiver.html#method.recv
-/// [`Sender`]: struct.Sender.html
-/// [`Receiver`]: struct.Receiver.html
-/// [`sync_channel`]: fn.sync_channel.html
-/// [`SendError`]: struct.SendError.html
-/// [`RecvError`]: struct.RecvError.html
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::mpsc::channel;
-/// use std::thread;
-///
-/// let (sender, receiver) = channel();
-///
-/// // Spawn off an expensive computation
-/// thread::spawn(move|| {
-/// #   fn expensive_computation() {}
-///     sender.send(expensive_computation()).unwrap();
-/// });
-///
-/// // Do some useful work for awhile
-///
-/// // Let's see what that answer was
-/// println!("{:?}", receiver.recv().unwrap());
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
-    let a = Arc::new(oneshot::Packet::new());
-    (Sender::new(Flavor::Oneshot(a.clone())), Receiver::new(Flavor::Oneshot(a)))
-}
-
-/// Creates a new synchronous, bounded channel.
-/// All data sent on the [`SyncSender`] will become available on the [`Receiver`]
-/// in the same order as it was sent. Like asynchronous [`channel`]s, the
-/// [`Receiver`] will block until a message becomes available. `sync_channel`
-/// differs greatly in the semantics of the sender, however.
-///
-/// This channel has an internal buffer on which messages will be queued.
-/// `bound` specifies the buffer size. When the internal buffer becomes full,
-/// future sends will *block* waiting for the buffer to open up. Note that a
-/// buffer size of 0 is valid, in which case this becomes "rendezvous channel"
-/// where each [`send`] will not return until a [`recv`] is paired with it.
-///
-/// The [`SyncSender`] can be cloned to [`send`] to the same channel multiple
-/// times, but only one [`Receiver`] is supported.
-///
-/// Like asynchronous channels, if the [`Receiver`] is disconnected while trying
-/// to [`send`] with the [`SyncSender`], the [`send`] method will return a
-/// [`SendError`]. Similarly, If the [`SyncSender`] is disconnected while trying
-/// to [`recv`], the [`recv`] method will return a [`RecvError`].
-///
-/// [`channel`]: fn.channel.html
-/// [`send`]: struct.SyncSender.html#method.send
-/// [`recv`]: struct.Receiver.html#method.recv
-/// [`SyncSender`]: struct.SyncSender.html
-/// [`Receiver`]: struct.Receiver.html
-/// [`SendError`]: struct.SendError.html
-/// [`RecvError`]: struct.RecvError.html
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::mpsc::sync_channel;
-/// use std::thread;
-///
-/// let (sender, receiver) = sync_channel(1);
-///
-/// // this returns immediately
-/// sender.send(1).unwrap();
-///
-/// thread::spawn(move|| {
-///     // this will block until the previous message has been received
-///     sender.send(2).unwrap();
-/// });
-///
-/// assert_eq!(receiver.recv().unwrap(), 1);
-/// assert_eq!(receiver.recv().unwrap(), 2);
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub fn sync_channel<T>(bound: usize) -> (SyncSender<T>, Receiver<T>) {
-    let a = Arc::new(sync::Packet::new(bound));
-    (SyncSender::new(a.clone()), Receiver::new(Flavor::Sync(a)))
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// Sender
-////////////////////////////////////////////////////////////////////////////////
-
-impl<T> Sender<T> {
-    fn new(inner: Flavor<T>) -> Sender<T> {
-        Sender { inner: UnsafeCell::new(inner) }
-    }
-
-    /// Attempts to send a value on this channel, returning it back if it could
-    /// not be sent.
-    ///
-    /// A successful send occurs when it is determined that the other end of
-    /// the channel has not hung up already. An unsuccessful send would be one
-    /// where the corresponding receiver has already been deallocated. Note
-    /// that a return value of [`Err`] means that the data will never be
-    /// received, but a return value of [`Ok`] does *not* mean that the data
-    /// will be received. It is possible for the corresponding receiver to
-    /// hang up immediately after this function returns [`Ok`].
-    ///
-    /// [`Err`]: ../../../std/result/enum.Result.html#variant.Err
-    /// [`Ok`]: ../../../std/result/enum.Result.html#variant.Ok
-    ///
-    /// This method will never block the current thread.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::mpsc::channel;
-    ///
-    /// let (tx, rx) = channel();
-    ///
-    /// // This send is always successful
-    /// tx.send(1).unwrap();
-    ///
-    /// // This send will fail because the receiver is gone
-    /// drop(rx);
-    /// assert_eq!(tx.send(1).unwrap_err().0, 1);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn send(&self, t: T) -> Result<(), SendError<T>> {
-        let (new_inner, ret) = match *unsafe { self.inner() } {
-            Flavor::Oneshot(ref p) => {
-                if !p.sent() {
-                    return p.send(t).map_err(SendError);
-                } else {
-                    let a = Arc::new(stream::Packet::new());
-                    let rx = Receiver::new(Flavor::Stream(a.clone()));
-                    match p.upgrade(rx) {
-                        oneshot::UpSuccess => {
-                            let ret = a.send(t);
-                            (a, ret)
-                        }
-                        oneshot::UpDisconnected => (a, Err(t)),
-                        oneshot::UpWoke(token) => {
-                            // This send cannot panic because the thread is
-                            // asleep (we're looking at it), so the receiver
-                            // can't go away.
-                            a.send(t).ok().unwrap();
-                            token.signal();
-                            (a, Ok(()))
-                        }
-                    }
-                }
-            }
-            Flavor::Stream(ref p) => return p.send(t).map_err(SendError),
-            Flavor::Shared(ref p) => return p.send(t).map_err(SendError),
-            Flavor::Sync(..) => unreachable!(),
-        };
-
-        unsafe {
-            let tmp = Sender::new(Flavor::Stream(new_inner));
-            mem::swap(self.inner_mut(), tmp.inner_mut());
-        }
-        ret.map_err(SendError)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Clone for Sender<T> {
-    fn clone(&self) -> Sender<T> {
-        let packet = match *unsafe { self.inner() } {
-            Flavor::Oneshot(ref p) => {
-                let a = Arc::new(shared::Packet::new());
-                {
-                    let guard = a.postinit_lock();
-                    let rx = Receiver::new(Flavor::Shared(a.clone()));
-                    let sleeper = match p.upgrade(rx) {
-                        oneshot::UpSuccess | oneshot::UpDisconnected => None,
-                        oneshot::UpWoke(task) => Some(task),
-                    };
-                    a.inherit_blocker(sleeper, guard);
-                }
-                a
-            }
-            Flavor::Stream(ref p) => {
-                let a = Arc::new(shared::Packet::new());
-                {
-                    let guard = a.postinit_lock();
-                    let rx = Receiver::new(Flavor::Shared(a.clone()));
-                    let sleeper = match p.upgrade(rx) {
-                        stream::UpSuccess | stream::UpDisconnected => None,
-                        stream::UpWoke(task) => Some(task),
-                    };
-                    a.inherit_blocker(sleeper, guard);
-                }
-                a
-            }
-            Flavor::Shared(ref p) => {
-                p.clone_chan();
-                return Sender::new(Flavor::Shared(p.clone()));
-            }
-            Flavor::Sync(..) => unreachable!(),
-        };
-
-        unsafe {
-            let tmp = Sender::new(Flavor::Shared(packet.clone()));
-            mem::swap(self.inner_mut(), tmp.inner_mut());
-        }
-        Sender::new(Flavor::Shared(packet))
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for Sender<T> {
-    fn drop(&mut self) {
-        match *unsafe { self.inner() } {
-            Flavor::Oneshot(ref p) => p.drop_chan(),
-            Flavor::Stream(ref p) => p.drop_chan(),
-            Flavor::Shared(ref p) => p.drop_chan(),
-            Flavor::Sync(..) => unreachable!(),
-        }
-    }
-}
-
-#[stable(feature = "mpsc_debug", since = "1.8.0")]
-impl<T> fmt::Debug for Sender<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Sender").finish()
-    }
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// SyncSender
-////////////////////////////////////////////////////////////////////////////////
-
-impl<T> SyncSender<T> {
-    fn new(inner: Arc<sync::Packet<T>>) -> SyncSender<T> {
-        SyncSender { inner }
-    }
-
-    /// Sends a value on this synchronous channel.
-    ///
-    /// This function will *block* until space in the internal buffer becomes
-    /// available or a receiver is available to hand off the message to.
-    ///
-    /// Note that a successful send does *not* guarantee that the receiver will
-    /// ever see the data if there is a buffer on this channel. Items may be
-    /// enqueued in the internal buffer for the receiver to receive at a later
-    /// time. If the buffer size is 0, however, the channel becomes a rendezvous
-    /// channel and it guarantees that the receiver has indeed received
-    /// the data if this function returns success.
-    ///
-    /// This function will never panic, but it may return [`Err`] if the
-    /// [`Receiver`] has disconnected and is no longer able to receive
-    /// information.
-    ///
-    /// [`Err`]: ../../../std/result/enum.Result.html#variant.Err
-    /// [`Receiver`]: ../../../std/sync/mpsc/struct.Receiver.html
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// use std::sync::mpsc::sync_channel;
-    /// use std::thread;
-    ///
-    /// // Create a rendezvous sync_channel with buffer size 0
-    /// let (sync_sender, receiver) = sync_channel(0);
-    ///
-    /// thread::spawn(move || {
-    ///    println!("sending message...");
-    ///    sync_sender.send(1).unwrap();
-    ///    // Thread is now blocked until the message is received
-    ///
-    ///    println!("...message received!");
-    /// });
-    ///
-    /// let msg = receiver.recv().unwrap();
-    /// assert_eq!(1, msg);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn send(&self, t: T) -> Result<(), SendError<T>> {
-        self.inner.send(t).map_err(SendError)
-    }
-
-    /// Attempts to send a value on this channel without blocking.
-    ///
-    /// This method differs from [`send`] by returning immediately if the
-    /// channel's buffer is full or no receiver is waiting to acquire some
-    /// data. Compared with [`send`], this function has two failure cases
-    /// instead of one (one for disconnection, one for a full buffer).
-    ///
-    /// See [`send`] for notes about guarantees of whether the
-    /// receiver has received the data or not if this function is successful.
-    ///
-    /// [`send`]: ../../../std/sync/mpsc/struct.SyncSender.html#method.send
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// use std::sync::mpsc::sync_channel;
-    /// use std::thread;
-    ///
-    /// // Create a sync_channel with buffer size 1
-    /// let (sync_sender, receiver) = sync_channel(1);
-    /// let sync_sender2 = sync_sender.clone();
-    ///
-    /// // First thread owns sync_sender
-    /// thread::spawn(move || {
-    ///     sync_sender.send(1).unwrap();
-    ///     sync_sender.send(2).unwrap();
-    ///     // Thread blocked
-    /// });
-    ///
-    /// // Second thread owns sync_sender2
-    /// thread::spawn(move || {
-    ///     // This will return an error and send
-    ///     // no message if the buffer is full
-    ///     let _ = sync_sender2.try_send(3);
-    /// });
-    ///
-    /// let mut msg;
-    /// msg = receiver.recv().unwrap();
-    /// println!("message {} received", msg);
-    ///
-    /// msg = receiver.recv().unwrap();
-    /// println!("message {} received", msg);
-    ///
-    /// // Third message may have never been sent
-    /// match receiver.try_recv() {
-    ///     Ok(msg) => println!("message {} received", msg),
-    ///     Err(_) => println!("the third message was never sent"),
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn try_send(&self, t: T) -> Result<(), TrySendError<T>> {
-        self.inner.try_send(t)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Clone for SyncSender<T> {
-    fn clone(&self) -> SyncSender<T> {
-        self.inner.clone_chan();
-        SyncSender::new(self.inner.clone())
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for SyncSender<T> {
-    fn drop(&mut self) {
-        self.inner.drop_chan();
-    }
-}
-
-#[stable(feature = "mpsc_debug", since = "1.8.0")]
-impl<T> fmt::Debug for SyncSender<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("SyncSender").finish()
-    }
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// Receiver
-////////////////////////////////////////////////////////////////////////////////
-
-impl<T> Receiver<T> {
-    fn new(inner: Flavor<T>) -> Receiver<T> {
-        Receiver { inner: UnsafeCell::new(inner) }
-    }
-
-    /// Attempts to return a pending value on this receiver without blocking.
-    ///
-    /// This method will never block the caller in order to wait for data to
-    /// become available. Instead, this will always return immediately with a
-    /// possible option of pending data on the channel.
-    ///
-    /// This is useful for a flavor of "optimistic check" before deciding to
-    /// block on a receiver.
-    ///
-    /// Compared with [`recv`], this function has two failure cases instead of one
-    /// (one for disconnection, one for an empty buffer).
-    ///
-    /// [`recv`]: struct.Receiver.html#method.recv
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// use std::sync::mpsc::{Receiver, channel};
-    ///
-    /// let (_, receiver): (_, Receiver<i32>) = channel();
-    ///
-    /// assert!(receiver.try_recv().is_err());
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn try_recv(&self) -> Result<T, TryRecvError> {
-        loop {
-            let new_port = match *unsafe { self.inner() } {
-                Flavor::Oneshot(ref p) => match p.try_recv() {
-                    Ok(t) => return Ok(t),
-                    Err(oneshot::Empty) => return Err(TryRecvError::Empty),
-                    Err(oneshot::Disconnected) => return Err(TryRecvError::Disconnected),
-                    Err(oneshot::Upgraded(rx)) => rx,
-                },
-                Flavor::Stream(ref p) => match p.try_recv() {
-                    Ok(t) => return Ok(t),
-                    Err(stream::Empty) => return Err(TryRecvError::Empty),
-                    Err(stream::Disconnected) => return Err(TryRecvError::Disconnected),
-                    Err(stream::Upgraded(rx)) => rx,
-                },
-                Flavor::Shared(ref p) => match p.try_recv() {
-                    Ok(t) => return Ok(t),
-                    Err(shared::Empty) => return Err(TryRecvError::Empty),
-                    Err(shared::Disconnected) => return Err(TryRecvError::Disconnected),
-                },
-                Flavor::Sync(ref p) => match p.try_recv() {
-                    Ok(t) => return Ok(t),
-                    Err(sync::Empty) => return Err(TryRecvError::Empty),
-                    Err(sync::Disconnected) => return Err(TryRecvError::Disconnected),
-                },
-            };
-            unsafe {
-                mem::swap(self.inner_mut(), new_port.inner_mut());
-            }
-        }
-    }
-
-    /// Attempts to wait for a value on this receiver, returning an error if the
-    /// corresponding channel has hung up.
-    ///
-    /// This function will always block the current thread if there is no data
-    /// available and it's possible for more data to be sent. Once a message is
-    /// sent to the corresponding [`Sender`] (or [`SyncSender`]), then this
-    /// receiver will wake up and return that message.
-    ///
-    /// If the corresponding [`Sender`] has disconnected, or it disconnects while
-    /// this call is blocking, this call will wake up and return [`Err`] to
-    /// indicate that no more messages can ever be received on this channel.
-    /// However, since channels are buffered, messages sent before the disconnect
-    /// will still be properly received.
-    ///
-    /// [`Sender`]: struct.Sender.html
-    /// [`SyncSender`]: struct.SyncSender.html
-    /// [`Err`]: ../../../std/result/enum.Result.html#variant.Err
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::mpsc;
-    /// use std::thread;
-    ///
-    /// let (send, recv) = mpsc::channel();
-    /// let handle = thread::spawn(move || {
-    ///     send.send(1u8).unwrap();
-    /// });
-    ///
-    /// handle.join().unwrap();
-    ///
-    /// assert_eq!(Ok(1), recv.recv());
-    /// ```
-    ///
-    /// Buffering behavior:
-    ///
-    /// ```
-    /// use std::sync::mpsc;
-    /// use std::thread;
-    /// use std::sync::mpsc::RecvError;
-    ///
-    /// let (send, recv) = mpsc::channel();
-    /// let handle = thread::spawn(move || {
-    ///     send.send(1u8).unwrap();
-    ///     send.send(2).unwrap();
-    ///     send.send(3).unwrap();
-    ///     drop(send);
-    /// });
-    ///
-    /// // wait for the thread to join so we ensure the sender is dropped
-    /// handle.join().unwrap();
-    ///
-    /// assert_eq!(Ok(1), recv.recv());
-    /// assert_eq!(Ok(2), recv.recv());
-    /// assert_eq!(Ok(3), recv.recv());
-    /// assert_eq!(Err(RecvError), recv.recv());
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn recv(&self) -> Result<T, RecvError> {
-        loop {
-            let new_port = match *unsafe { self.inner() } {
-                Flavor::Oneshot(ref p) => match p.recv(None) {
-                    Ok(t) => return Ok(t),
-                    Err(oneshot::Disconnected) => return Err(RecvError),
-                    Err(oneshot::Upgraded(rx)) => rx,
-                    Err(oneshot::Empty) => unreachable!(),
-                },
-                Flavor::Stream(ref p) => match p.recv(None) {
-                    Ok(t) => return Ok(t),
-                    Err(stream::Disconnected) => return Err(RecvError),
-                    Err(stream::Upgraded(rx)) => rx,
-                    Err(stream::Empty) => unreachable!(),
-                },
-                Flavor::Shared(ref p) => match p.recv(None) {
-                    Ok(t) => return Ok(t),
-                    Err(shared::Disconnected) => return Err(RecvError),
-                    Err(shared::Empty) => unreachable!(),
-                },
-                Flavor::Sync(ref p) => return p.recv(None).map_err(|_| RecvError),
-            };
-            unsafe {
-                mem::swap(self.inner_mut(), new_port.inner_mut());
-            }
-        }
-    }
-
-    /// Attempts to wait for a value on this receiver, returning an error if the
-    /// corresponding channel has hung up, or if it waits more than `timeout`.
-    ///
-    /// This function will always block the current thread if there is no data
-    /// available and it's possible for more data to be sent. Once a message is
-    /// sent to the corresponding [`Sender`] (or [`SyncSender`]), then this
-    /// receiver will wake up and return that message.
-    ///
-    /// If the corresponding [`Sender`] has disconnected, or it disconnects while
-    /// this call is blocking, this call will wake up and return [`Err`] to
-    /// indicate that no more messages can ever be received on this channel.
-    /// However, since channels are buffered, messages sent before the disconnect
-    /// will still be properly received.
-    ///
-    /// [`Sender`]: struct.Sender.html
-    /// [`SyncSender`]: struct.SyncSender.html
-    /// [`Err`]: ../../../std/result/enum.Result.html#variant.Err
-    ///
-    /// # Known Issues
-    ///
-    /// There is currently a known issue (see [`#39364`]) that causes `recv_timeout`
-    /// to panic unexpectedly with the following example:
-    ///
-    /// ```no_run
-    /// use std::sync::mpsc::channel;
-    /// use std::thread;
-    /// use std::time::Duration;
-    ///
-    /// let (tx, rx) = channel::<String>();
-    ///
-    /// thread::spawn(move || {
-    ///     let d = Duration::from_millis(10);
-    ///     loop {
-    ///         println!("recv");
-    ///         let _r = rx.recv_timeout(d);
-    ///     }
-    /// });
-    ///
-    /// thread::sleep(Duration::from_millis(100));
-    /// let _c1 = tx.clone();
-    ///
-    /// thread::sleep(Duration::from_secs(1));
-    /// ```
-    ///
-    /// [`#39364`]: https://github.com/rust-lang/rust/issues/39364
-    ///
-    /// # Examples
-    ///
-    /// Successfully receiving value before encountering timeout:
-    ///
-    /// ```no_run
-    /// use std::thread;
-    /// use std::time::Duration;
-    /// use std::sync::mpsc;
-    ///
-    /// let (send, recv) = mpsc::channel();
-    ///
-    /// thread::spawn(move || {
-    ///     send.send('a').unwrap();
-    /// });
-    ///
-    /// assert_eq!(
-    ///     recv.recv_timeout(Duration::from_millis(400)),
-    ///     Ok('a')
-    /// );
-    /// ```
-    ///
-    /// Receiving an error upon reaching timeout:
-    ///
-    /// ```no_run
-    /// use std::thread;
-    /// use std::time::Duration;
-    /// use std::sync::mpsc;
-    ///
-    /// let (send, recv) = mpsc::channel();
-    ///
-    /// thread::spawn(move || {
-    ///     thread::sleep(Duration::from_millis(800));
-    ///     send.send('a').unwrap();
-    /// });
-    ///
-    /// assert_eq!(
-    ///     recv.recv_timeout(Duration::from_millis(400)),
-    ///     Err(mpsc::RecvTimeoutError::Timeout)
-    /// );
-    /// ```
-    #[stable(feature = "mpsc_recv_timeout", since = "1.12.0")]
-    pub fn recv_timeout(&self, timeout: Duration) -> Result<T, RecvTimeoutError> {
-        // Do an optimistic try_recv to avoid the performance impact of
-        // Instant::now() in the full-channel case.
-        match self.try_recv() {
-            Ok(result) => Ok(result),
-            Err(TryRecvError::Disconnected) => Err(RecvTimeoutError::Disconnected),
-            Err(TryRecvError::Empty) => match Instant::now().checked_add(timeout) {
-                Some(deadline) => self.recv_deadline(deadline),
-                // So far in the future that it's practically the same as waiting indefinitely.
-                None => self.recv().map_err(RecvTimeoutError::from),
-            },
-        }
-    }
-
-    /// Attempts to wait for a value on this receiver, returning an error if the
-    /// corresponding channel has hung up, or if `deadline` is reached.
-    ///
-    /// This function will always block the current thread if there is no data
-    /// available and it's possible for more data to be sent. Once a message is
-    /// sent to the corresponding [`Sender`] (or [`SyncSender`]), then this
-    /// receiver will wake up and return that message.
-    ///
-    /// If the corresponding [`Sender`] has disconnected, or it disconnects while
-    /// this call is blocking, this call will wake up and return [`Err`] to
-    /// indicate that no more messages can ever be received on this channel.
-    /// However, since channels are buffered, messages sent before the disconnect
-    /// will still be properly received.
-    ///
-    /// [`Sender`]: struct.Sender.html
-    /// [`SyncSender`]: struct.SyncSender.html
-    /// [`Err`]: ../../../std/result/enum.Result.html#variant.Err
-    ///
-    /// # Examples
-    ///
-    /// Successfully receiving value before reaching deadline:
-    ///
-    /// ```no_run
-    /// #![feature(deadline_api)]
-    /// use std::thread;
-    /// use std::time::{Duration, Instant};
-    /// use std::sync::mpsc;
-    ///
-    /// let (send, recv) = mpsc::channel();
-    ///
-    /// thread::spawn(move || {
-    ///     send.send('a').unwrap();
-    /// });
-    ///
-    /// assert_eq!(
-    ///     recv.recv_deadline(Instant::now() + Duration::from_millis(400)),
-    ///     Ok('a')
-    /// );
-    /// ```
-    ///
-    /// Receiving an error upon reaching deadline:
-    ///
-    /// ```no_run
-    /// #![feature(deadline_api)]
-    /// use std::thread;
-    /// use std::time::{Duration, Instant};
-    /// use std::sync::mpsc;
-    ///
-    /// let (send, recv) = mpsc::channel();
-    ///
-    /// thread::spawn(move || {
-    ///     thread::sleep(Duration::from_millis(800));
-    ///     send.send('a').unwrap();
-    /// });
-    ///
-    /// assert_eq!(
-    ///     recv.recv_deadline(Instant::now() + Duration::from_millis(400)),
-    ///     Err(mpsc::RecvTimeoutError::Timeout)
-    /// );
-    /// ```
-    #[unstable(feature = "deadline_api", issue = "46316")]
-    pub fn recv_deadline(&self, deadline: Instant) -> Result<T, RecvTimeoutError> {
-        use self::RecvTimeoutError::*;
-
-        loop {
-            let port_or_empty = match *unsafe { self.inner() } {
-                Flavor::Oneshot(ref p) => match p.recv(Some(deadline)) {
-                    Ok(t) => return Ok(t),
-                    Err(oneshot::Disconnected) => return Err(Disconnected),
-                    Err(oneshot::Upgraded(rx)) => Some(rx),
-                    Err(oneshot::Empty) => None,
-                },
-                Flavor::Stream(ref p) => match p.recv(Some(deadline)) {
-                    Ok(t) => return Ok(t),
-                    Err(stream::Disconnected) => return Err(Disconnected),
-                    Err(stream::Upgraded(rx)) => Some(rx),
-                    Err(stream::Empty) => None,
-                },
-                Flavor::Shared(ref p) => match p.recv(Some(deadline)) {
-                    Ok(t) => return Ok(t),
-                    Err(shared::Disconnected) => return Err(Disconnected),
-                    Err(shared::Empty) => None,
-                },
-                Flavor::Sync(ref p) => match p.recv(Some(deadline)) {
-                    Ok(t) => return Ok(t),
-                    Err(sync::Disconnected) => return Err(Disconnected),
-                    Err(sync::Empty) => None,
-                },
-            };
-
-            if let Some(new_port) = port_or_empty {
-                unsafe {
-                    mem::swap(self.inner_mut(), new_port.inner_mut());
-                }
-            }
-
-            // If we're already passed the deadline, and we're here without
-            // data, return a timeout, else try again.
-            if Instant::now() >= deadline {
-                return Err(Timeout);
-            }
-        }
-    }
-
-    /// Returns an iterator that will block waiting for messages, but never
-    /// [`panic!`]. It will return [`None`] when the channel has hung up.
-    ///
-    /// [`panic!`]: ../../../std/macro.panic.html
-    /// [`None`]: ../../../std/option/enum.Option.html#variant.None
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// use std::sync::mpsc::channel;
-    /// use std::thread;
-    ///
-    /// let (send, recv) = channel();
-    ///
-    /// thread::spawn(move || {
-    ///     send.send(1).unwrap();
-    ///     send.send(2).unwrap();
-    ///     send.send(3).unwrap();
-    /// });
-    ///
-    /// let mut iter = recv.iter();
-    /// assert_eq!(iter.next(), Some(1));
-    /// assert_eq!(iter.next(), Some(2));
-    /// assert_eq!(iter.next(), Some(3));
-    /// assert_eq!(iter.next(), None);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn iter(&self) -> Iter<'_, T> {
-        Iter { rx: self }
-    }
-
-    /// Returns an iterator that will attempt to yield all pending values.
-    /// It will return `None` if there are no more pending values or if the
-    /// channel has hung up. The iterator will never [`panic!`] or block the
-    /// user by waiting for values.
-    ///
-    /// [`panic!`]: ../../../std/macro.panic.html
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// use std::sync::mpsc::channel;
-    /// use std::thread;
-    /// use std::time::Duration;
-    ///
-    /// let (sender, receiver) = channel();
-    ///
-    /// // nothing is in the buffer yet
-    /// assert!(receiver.try_iter().next().is_none());
-    ///
-    /// thread::spawn(move || {
-    ///     thread::sleep(Duration::from_secs(1));
-    ///     sender.send(1).unwrap();
-    ///     sender.send(2).unwrap();
-    ///     sender.send(3).unwrap();
-    /// });
-    ///
-    /// // nothing is in the buffer yet
-    /// assert!(receiver.try_iter().next().is_none());
-    ///
-    /// // block for two seconds
-    /// thread::sleep(Duration::from_secs(2));
-    ///
-    /// let mut iter = receiver.try_iter();
-    /// assert_eq!(iter.next(), Some(1));
-    /// assert_eq!(iter.next(), Some(2));
-    /// assert_eq!(iter.next(), Some(3));
-    /// assert_eq!(iter.next(), None);
-    /// ```
-    #[stable(feature = "receiver_try_iter", since = "1.15.0")]
-    pub fn try_iter(&self) -> TryIter<'_, T> {
-        TryIter { rx: self }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Iterator for Iter<'a, T> {
-    type Item = T;
-
-    fn next(&mut self) -> Option<T> {
-        self.rx.recv().ok()
-    }
-}
-
-#[stable(feature = "receiver_try_iter", since = "1.15.0")]
-impl<'a, T> Iterator for TryIter<'a, T> {
-    type Item = T;
-
-    fn next(&mut self) -> Option<T> {
-        self.rx.try_recv().ok()
-    }
-}
-
-#[stable(feature = "receiver_into_iter", since = "1.1.0")]
-impl<'a, T> IntoIterator for &'a Receiver<T> {
-    type Item = T;
-    type IntoIter = Iter<'a, T>;
-
-    fn into_iter(self) -> Iter<'a, T> {
-        self.iter()
-    }
-}
-
-#[stable(feature = "receiver_into_iter", since = "1.1.0")]
-impl<T> Iterator for IntoIter<T> {
-    type Item = T;
-    fn next(&mut self) -> Option<T> {
-        self.rx.recv().ok()
-    }
-}
-
-#[stable(feature = "receiver_into_iter", since = "1.1.0")]
-impl<T> IntoIterator for Receiver<T> {
-    type Item = T;
-    type IntoIter = IntoIter<T>;
-
-    fn into_iter(self) -> IntoIter<T> {
-        IntoIter { rx: self }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for Receiver<T> {
-    fn drop(&mut self) {
-        match *unsafe { self.inner() } {
-            Flavor::Oneshot(ref p) => p.drop_port(),
-            Flavor::Stream(ref p) => p.drop_port(),
-            Flavor::Shared(ref p) => p.drop_port(),
-            Flavor::Sync(ref p) => p.drop_port(),
-        }
-    }
-}
-
-#[stable(feature = "mpsc_debug", since = "1.8.0")]
-impl<T> fmt::Debug for Receiver<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Receiver").finish()
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Debug for SendError<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        "SendError(..)".fmt(f)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Display for SendError<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        "sending on a closed channel".fmt(f)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> error::Error for SendError<T> {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "sending on a closed channel"
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Debug for TrySendError<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            TrySendError::Full(..) => "Full(..)".fmt(f),
-            TrySendError::Disconnected(..) => "Disconnected(..)".fmt(f),
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Display for TrySendError<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            TrySendError::Full(..) => "sending on a full channel".fmt(f),
-            TrySendError::Disconnected(..) => "sending on a closed channel".fmt(f),
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Send> error::Error for TrySendError<T> {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        match *self {
-            TrySendError::Full(..) => "sending on a full channel",
-            TrySendError::Disconnected(..) => "sending on a closed channel",
-        }
-    }
-}
-
-#[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
-impl<T> From<SendError<T>> for TrySendError<T> {
-    fn from(err: SendError<T>) -> TrySendError<T> {
-        match err {
-            SendError(t) => TrySendError::Disconnected(t),
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl fmt::Display for RecvError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        "receiving on a closed channel".fmt(f)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl error::Error for RecvError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "receiving on a closed channel"
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl fmt::Display for TryRecvError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            TryRecvError::Empty => "receiving on an empty channel".fmt(f),
-            TryRecvError::Disconnected => "receiving on a closed channel".fmt(f),
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl error::Error for TryRecvError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        match *self {
-            TryRecvError::Empty => "receiving on an empty channel",
-            TryRecvError::Disconnected => "receiving on a closed channel",
-        }
-    }
-}
-
-#[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
-impl From<RecvError> for TryRecvError {
-    fn from(err: RecvError) -> TryRecvError {
-        match err {
-            RecvError => TryRecvError::Disconnected,
-        }
-    }
-}
-
-#[stable(feature = "mpsc_recv_timeout_error", since = "1.15.0")]
-impl fmt::Display for RecvTimeoutError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            RecvTimeoutError::Timeout => "timed out waiting on channel".fmt(f),
-            RecvTimeoutError::Disconnected => "channel is empty and sending half is closed".fmt(f),
-        }
-    }
-}
-
-#[stable(feature = "mpsc_recv_timeout_error", since = "1.15.0")]
-impl error::Error for RecvTimeoutError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        match *self {
-            RecvTimeoutError::Timeout => "timed out waiting on channel",
-            RecvTimeoutError::Disconnected => "channel is empty and sending half is closed",
-        }
-    }
-}
-
-#[stable(feature = "mpsc_error_conversions", since = "1.24.0")]
-impl From<RecvError> for RecvTimeoutError {
-    fn from(err: RecvError) -> RecvTimeoutError {
-        match err {
-            RecvError => RecvTimeoutError::Disconnected,
-        }
-    }
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod tests {
-    use super::*;
-    use crate::env;
-    use crate::thread;
-    use crate::time::{Duration, Instant};
-
-    pub fn stress_factor() -> usize {
-        match env::var("RUST_TEST_STRESS") {
-            Ok(val) => val.parse().unwrap(),
-            Err(..) => 1,
-        }
-    }
-
-    #[test]
-    fn smoke() {
-        let (tx, rx) = channel::<i32>();
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv().unwrap(), 1);
-    }
-
-    #[test]
-    fn drop_full() {
-        let (tx, _rx) = channel::<Box<isize>>();
-        tx.send(box 1).unwrap();
-    }
-
-    #[test]
-    fn drop_full_shared() {
-        let (tx, _rx) = channel::<Box<isize>>();
-        drop(tx.clone());
-        drop(tx.clone());
-        tx.send(box 1).unwrap();
-    }
-
-    #[test]
-    fn smoke_shared() {
-        let (tx, rx) = channel::<i32>();
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv().unwrap(), 1);
-        let tx = tx.clone();
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv().unwrap(), 1);
-    }
-
-    #[test]
-    fn smoke_threads() {
-        let (tx, rx) = channel::<i32>();
-        let _t = thread::spawn(move || {
-            tx.send(1).unwrap();
-        });
-        assert_eq!(rx.recv().unwrap(), 1);
-    }
-
-    #[test]
-    fn smoke_port_gone() {
-        let (tx, rx) = channel::<i32>();
-        drop(rx);
-        assert!(tx.send(1).is_err());
-    }
-
-    #[test]
-    fn smoke_shared_port_gone() {
-        let (tx, rx) = channel::<i32>();
-        drop(rx);
-        assert!(tx.send(1).is_err())
-    }
-
-    #[test]
-    fn smoke_shared_port_gone2() {
-        let (tx, rx) = channel::<i32>();
-        drop(rx);
-        let tx2 = tx.clone();
-        drop(tx);
-        assert!(tx2.send(1).is_err());
-    }
-
-    #[test]
-    fn port_gone_concurrent() {
-        let (tx, rx) = channel::<i32>();
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap();
-        });
-        while tx.send(1).is_ok() {}
-    }
-
-    #[test]
-    fn port_gone_concurrent_shared() {
-        let (tx, rx) = channel::<i32>();
-        let tx2 = tx.clone();
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap();
-        });
-        while tx.send(1).is_ok() && tx2.send(1).is_ok() {}
-    }
-
-    #[test]
-    fn smoke_chan_gone() {
-        let (tx, rx) = channel::<i32>();
-        drop(tx);
-        assert!(rx.recv().is_err());
-    }
-
-    #[test]
-    fn smoke_chan_gone_shared() {
-        let (tx, rx) = channel::<()>();
-        let tx2 = tx.clone();
-        drop(tx);
-        drop(tx2);
-        assert!(rx.recv().is_err());
-    }
-
-    #[test]
-    fn chan_gone_concurrent() {
-        let (tx, rx) = channel::<i32>();
-        let _t = thread::spawn(move || {
-            tx.send(1).unwrap();
-            tx.send(1).unwrap();
-        });
-        while rx.recv().is_ok() {}
-    }
-
-    #[test]
-    fn stress() {
-        let (tx, rx) = channel::<i32>();
-        let t = thread::spawn(move || {
-            for _ in 0..10000 {
-                tx.send(1).unwrap();
-            }
-        });
-        for _ in 0..10000 {
-            assert_eq!(rx.recv().unwrap(), 1);
-        }
-        t.join().ok().expect("thread panicked");
-    }
-
-    #[test]
-    fn stress_shared() {
-        const AMT: u32 = 10000;
-        const NTHREADS: u32 = 8;
-        let (tx, rx) = channel::<i32>();
-
-        let t = thread::spawn(move || {
-            for _ in 0..AMT * NTHREADS {
-                assert_eq!(rx.recv().unwrap(), 1);
-            }
-            match rx.try_recv() {
-                Ok(..) => panic!(),
-                _ => {}
-            }
-        });
-
-        for _ in 0..NTHREADS {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                for _ in 0..AMT {
-                    tx.send(1).unwrap();
-                }
-            });
-        }
-        drop(tx);
-        t.join().ok().expect("thread panicked");
-    }
-
-    #[test]
-    fn send_from_outside_runtime() {
-        let (tx1, rx1) = channel::<()>();
-        let (tx2, rx2) = channel::<i32>();
-        let t1 = thread::spawn(move || {
-            tx1.send(()).unwrap();
-            for _ in 0..40 {
-                assert_eq!(rx2.recv().unwrap(), 1);
-            }
-        });
-        rx1.recv().unwrap();
-        let t2 = thread::spawn(move || {
-            for _ in 0..40 {
-                tx2.send(1).unwrap();
-            }
-        });
-        t1.join().ok().expect("thread panicked");
-        t2.join().ok().expect("thread panicked");
-    }
-
-    #[test]
-    fn recv_from_outside_runtime() {
-        let (tx, rx) = channel::<i32>();
-        let t = thread::spawn(move || {
-            for _ in 0..40 {
-                assert_eq!(rx.recv().unwrap(), 1);
-            }
-        });
-        for _ in 0..40 {
-            tx.send(1).unwrap();
-        }
-        t.join().ok().expect("thread panicked");
-    }
-
-    #[test]
-    fn no_runtime() {
-        let (tx1, rx1) = channel::<i32>();
-        let (tx2, rx2) = channel::<i32>();
-        let t1 = thread::spawn(move || {
-            assert_eq!(rx1.recv().unwrap(), 1);
-            tx2.send(2).unwrap();
-        });
-        let t2 = thread::spawn(move || {
-            tx1.send(1).unwrap();
-            assert_eq!(rx2.recv().unwrap(), 2);
-        });
-        t1.join().ok().expect("thread panicked");
-        t2.join().ok().expect("thread panicked");
-    }
-
-    #[test]
-    fn oneshot_single_thread_close_port_first() {
-        // Simple test of closing without sending
-        let (_tx, rx) = channel::<i32>();
-        drop(rx);
-    }
-
-    #[test]
-    fn oneshot_single_thread_close_chan_first() {
-        // Simple test of closing without sending
-        let (tx, _rx) = channel::<i32>();
-        drop(tx);
-    }
-
-    #[test]
-    fn oneshot_single_thread_send_port_close() {
-        // Testing that the sender cleans up the payload if receiver is closed
-        let (tx, rx) = channel::<Box<i32>>();
-        drop(rx);
-        assert!(tx.send(box 0).is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_recv_chan_close() {
-        // Receiving on a closed chan will panic
-        let res = thread::spawn(move || {
-            let (tx, rx) = channel::<i32>();
-            drop(tx);
-            rx.recv().unwrap();
-        })
-        .join();
-        // What is our res?
-        assert!(res.is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_send_then_recv() {
-        let (tx, rx) = channel::<Box<i32>>();
-        tx.send(box 10).unwrap();
-        assert!(*rx.recv().unwrap() == 10);
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_send_open() {
-        let (tx, rx) = channel::<i32>();
-        assert!(tx.send(10).is_ok());
-        assert!(rx.recv().unwrap() == 10);
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_send_closed() {
-        let (tx, rx) = channel::<i32>();
-        drop(rx);
-        assert!(tx.send(10).is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_recv_open() {
-        let (tx, rx) = channel::<i32>();
-        tx.send(10).unwrap();
-        assert!(rx.recv() == Ok(10));
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_recv_closed() {
-        let (tx, rx) = channel::<i32>();
-        drop(tx);
-        assert!(rx.recv().is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_peek_data() {
-        let (tx, rx) = channel::<i32>();
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
-        tx.send(10).unwrap();
-        assert_eq!(rx.try_recv(), Ok(10));
-    }
-
-    #[test]
-    fn oneshot_single_thread_peek_close() {
-        let (tx, rx) = channel::<i32>();
-        drop(tx);
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
-    }
-
-    #[test]
-    fn oneshot_single_thread_peek_open() {
-        let (_tx, rx) = channel::<i32>();
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
-    }
-
-    #[test]
-    fn oneshot_multi_task_recv_then_send() {
-        let (tx, rx) = channel::<Box<i32>>();
-        let _t = thread::spawn(move || {
-            assert!(*rx.recv().unwrap() == 10);
-        });
-
-        tx.send(box 10).unwrap();
-    }
-
-    #[test]
-    fn oneshot_multi_task_recv_then_close() {
-        let (tx, rx) = channel::<Box<i32>>();
-        let _t = thread::spawn(move || {
-            drop(tx);
-        });
-        let res = thread::spawn(move || {
-            assert!(*rx.recv().unwrap() == 10);
-        })
-        .join();
-        assert!(res.is_err());
-    }
-
-    #[test]
-    fn oneshot_multi_thread_close_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = channel::<i32>();
-            let _t = thread::spawn(move || {
-                drop(rx);
-            });
-            drop(tx);
-        }
-    }
-
-    #[test]
-    fn oneshot_multi_thread_send_close_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = channel::<i32>();
-            let _t = thread::spawn(move || {
-                drop(rx);
-            });
-            let _ = thread::spawn(move || {
-                tx.send(1).unwrap();
-            })
-            .join();
-        }
-    }
-
-    #[test]
-    fn oneshot_multi_thread_recv_close_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = channel::<i32>();
-            thread::spawn(move || {
-                let res = thread::spawn(move || {
-                    rx.recv().unwrap();
-                })
-                .join();
-                assert!(res.is_err());
-            });
-            let _t = thread::spawn(move || {
-                thread::spawn(move || {
-                    drop(tx);
-                });
-            });
-        }
-    }
-
-    #[test]
-    fn oneshot_multi_thread_send_recv_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = channel::<Box<isize>>();
-            let _t = thread::spawn(move || {
-                tx.send(box 10).unwrap();
-            });
-            assert!(*rx.recv().unwrap() == 10);
-        }
-    }
-
-    #[test]
-    fn stream_send_recv_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = channel();
-
-            send(tx, 0);
-            recv(rx, 0);
-
-            fn send(tx: Sender<Box<i32>>, i: i32) {
-                if i == 10 {
-                    return;
-                }
-
-                thread::spawn(move || {
-                    tx.send(box i).unwrap();
-                    send(tx, i + 1);
-                });
-            }
-
-            fn recv(rx: Receiver<Box<i32>>, i: i32) {
-                if i == 10 {
-                    return;
-                }
-
-                thread::spawn(move || {
-                    assert!(*rx.recv().unwrap() == i);
-                    recv(rx, i + 1);
-                });
-            }
-        }
-    }
-
-    #[test]
-    fn oneshot_single_thread_recv_timeout() {
-        let (tx, rx) = channel();
-        tx.send(()).unwrap();
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(()));
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Err(RecvTimeoutError::Timeout));
-        tx.send(()).unwrap();
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(()));
-    }
-
-    #[test]
-    fn stress_recv_timeout_two_threads() {
-        let (tx, rx) = channel();
-        let stress = stress_factor() + 100;
-        let timeout = Duration::from_millis(100);
-
-        thread::spawn(move || {
-            for i in 0..stress {
-                if i % 2 == 0 {
-                    thread::sleep(timeout * 2);
-                }
-                tx.send(1usize).unwrap();
-            }
-        });
-
-        let mut recv_count = 0;
-        loop {
-            match rx.recv_timeout(timeout) {
-                Ok(n) => {
-                    assert_eq!(n, 1usize);
-                    recv_count += 1;
-                }
-                Err(RecvTimeoutError::Timeout) => continue,
-                Err(RecvTimeoutError::Disconnected) => break,
-            }
-        }
-
-        assert_eq!(recv_count, stress);
-    }
-
-    #[test]
-    fn recv_timeout_upgrade() {
-        let (tx, rx) = channel::<()>();
-        let timeout = Duration::from_millis(1);
-        let _tx_clone = tx.clone();
-
-        let start = Instant::now();
-        assert_eq!(rx.recv_timeout(timeout), Err(RecvTimeoutError::Timeout));
-        assert!(Instant::now() >= start + timeout);
-    }
-
-    #[test]
-    fn stress_recv_timeout_shared() {
-        let (tx, rx) = channel();
-        let stress = stress_factor() + 100;
-
-        for i in 0..stress {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                thread::sleep(Duration::from_millis(i as u64 * 10));
-                tx.send(1usize).unwrap();
-            });
-        }
-
-        drop(tx);
-
-        let mut recv_count = 0;
-        loop {
-            match rx.recv_timeout(Duration::from_millis(10)) {
-                Ok(n) => {
-                    assert_eq!(n, 1usize);
-                    recv_count += 1;
-                }
-                Err(RecvTimeoutError::Timeout) => continue,
-                Err(RecvTimeoutError::Disconnected) => break,
-            }
-        }
-
-        assert_eq!(recv_count, stress);
-    }
-
-    #[test]
-    fn very_long_recv_timeout_wont_panic() {
-        let (tx, rx) = channel::<()>();
-        let join_handle = thread::spawn(move || rx.recv_timeout(Duration::from_secs(u64::MAX)));
-        thread::sleep(Duration::from_secs(1));
-        assert!(tx.send(()).is_ok());
-        assert_eq!(join_handle.join().unwrap(), Ok(()));
-    }
-
-    #[test]
-    fn recv_a_lot() {
-        // Regression test that we don't run out of stack in scheduler context
-        let (tx, rx) = channel();
-        for _ in 0..10000 {
-            tx.send(()).unwrap();
-        }
-        for _ in 0..10000 {
-            rx.recv().unwrap();
-        }
-    }
-
-    #[test]
-    fn shared_recv_timeout() {
-        let (tx, rx) = channel();
-        let total = 5;
-        for _ in 0..total {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                tx.send(()).unwrap();
-            });
-        }
-
-        for _ in 0..total {
-            rx.recv().unwrap();
-        }
-
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Err(RecvTimeoutError::Timeout));
-        tx.send(()).unwrap();
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(()));
-    }
-
-    #[test]
-    fn shared_chan_stress() {
-        let (tx, rx) = channel();
-        let total = stress_factor() + 100;
-        for _ in 0..total {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                tx.send(()).unwrap();
-            });
-        }
-
-        for _ in 0..total {
-            rx.recv().unwrap();
-        }
-    }
-
-    #[test]
-    fn test_nested_recv_iter() {
-        let (tx, rx) = channel::<i32>();
-        let (total_tx, total_rx) = channel::<i32>();
-
-        let _t = thread::spawn(move || {
-            let mut acc = 0;
-            for x in rx.iter() {
-                acc += x;
-            }
-            total_tx.send(acc).unwrap();
-        });
-
-        tx.send(3).unwrap();
-        tx.send(1).unwrap();
-        tx.send(2).unwrap();
-        drop(tx);
-        assert_eq!(total_rx.recv().unwrap(), 6);
-    }
-
-    #[test]
-    fn test_recv_iter_break() {
-        let (tx, rx) = channel::<i32>();
-        let (count_tx, count_rx) = channel();
-
-        let _t = thread::spawn(move || {
-            let mut count = 0;
-            for x in rx.iter() {
-                if count >= 3 {
-                    break;
-                } else {
-                    count += x;
-                }
-            }
-            count_tx.send(count).unwrap();
-        });
-
-        tx.send(2).unwrap();
-        tx.send(2).unwrap();
-        tx.send(2).unwrap();
-        let _ = tx.send(2);
-        drop(tx);
-        assert_eq!(count_rx.recv().unwrap(), 4);
-    }
-
-    #[test]
-    fn test_recv_try_iter() {
-        let (request_tx, request_rx) = channel();
-        let (response_tx, response_rx) = channel();
-
-        // Request `x`s until we have `6`.
-        let t = thread::spawn(move || {
-            let mut count = 0;
-            loop {
-                for x in response_rx.try_iter() {
-                    count += x;
-                    if count == 6 {
-                        return count;
-                    }
-                }
-                request_tx.send(()).unwrap();
-            }
-        });
-
-        for _ in request_rx.iter() {
-            if response_tx.send(2).is_err() {
-                break;
-            }
-        }
-
-        assert_eq!(t.join().unwrap(), 6);
-    }
-
-    #[test]
-    fn test_recv_into_iter_owned() {
-        let mut iter = {
-            let (tx, rx) = channel::<i32>();
-            tx.send(1).unwrap();
-            tx.send(2).unwrap();
-
-            rx.into_iter()
-        };
-        assert_eq!(iter.next().unwrap(), 1);
-        assert_eq!(iter.next().unwrap(), 2);
-        assert_eq!(iter.next().is_none(), true);
-    }
-
-    #[test]
-    fn test_recv_into_iter_borrowed() {
-        let (tx, rx) = channel::<i32>();
-        tx.send(1).unwrap();
-        tx.send(2).unwrap();
-        drop(tx);
-        let mut iter = (&rx).into_iter();
-        assert_eq!(iter.next().unwrap(), 1);
-        assert_eq!(iter.next().unwrap(), 2);
-        assert_eq!(iter.next().is_none(), true);
-    }
-
-    #[test]
-    fn try_recv_states() {
-        let (tx1, rx1) = channel::<i32>();
-        let (tx2, rx2) = channel::<()>();
-        let (tx3, rx3) = channel::<()>();
-        let _t = thread::spawn(move || {
-            rx2.recv().unwrap();
-            tx1.send(1).unwrap();
-            tx3.send(()).unwrap();
-            rx2.recv().unwrap();
-            drop(tx1);
-            tx3.send(()).unwrap();
-        });
-
-        assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
-        tx2.send(()).unwrap();
-        rx3.recv().unwrap();
-        assert_eq!(rx1.try_recv(), Ok(1));
-        assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
-        tx2.send(()).unwrap();
-        rx3.recv().unwrap();
-        assert_eq!(rx1.try_recv(), Err(TryRecvError::Disconnected));
-    }
-
-    // This bug used to end up in a livelock inside of the Receiver destructor
-    // because the internal state of the Shared packet was corrupted
-    #[test]
-    fn destroy_upgraded_shared_port_when_sender_still_active() {
-        let (tx, rx) = channel();
-        let (tx2, rx2) = channel();
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap(); // wait on a oneshot
-            drop(rx); // destroy a shared
-            tx2.send(()).unwrap();
-        });
-        // make sure the other thread has gone to sleep
-        for _ in 0..5000 {
-            thread::yield_now();
-        }
-
-        // upgrade to a shared chan and send a message
-        let t = tx.clone();
-        drop(tx);
-        t.send(()).unwrap();
-
-        // wait for the child thread to exit before we exit
-        rx2.recv().unwrap();
-    }
-
-    #[test]
-    fn issue_32114() {
-        let (tx, _) = channel();
-        let _ = tx.send(123);
-        assert_eq!(tx.send(123), Err(SendError(123)));
-    }
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod sync_tests {
-    use super::*;
-    use crate::env;
-    use crate::thread;
-    use crate::time::Duration;
-
-    pub fn stress_factor() -> usize {
-        match env::var("RUST_TEST_STRESS") {
-            Ok(val) => val.parse().unwrap(),
-            Err(..) => 1,
-        }
-    }
-
-    #[test]
-    fn smoke() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv().unwrap(), 1);
-    }
-
-    #[test]
-    fn drop_full() {
-        let (tx, _rx) = sync_channel::<Box<isize>>(1);
-        tx.send(box 1).unwrap();
-    }
-
-    #[test]
-    fn smoke_shared() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv().unwrap(), 1);
-        let tx = tx.clone();
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv().unwrap(), 1);
-    }
-
-    #[test]
-    fn recv_timeout() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Err(RecvTimeoutError::Timeout));
-        tx.send(1).unwrap();
-        assert_eq!(rx.recv_timeout(Duration::from_millis(1)), Ok(1));
-    }
-
-    #[test]
-    fn smoke_threads() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let _t = thread::spawn(move || {
-            tx.send(1).unwrap();
-        });
-        assert_eq!(rx.recv().unwrap(), 1);
-    }
-
-    #[test]
-    fn smoke_port_gone() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        drop(rx);
-        assert!(tx.send(1).is_err());
-    }
-
-    #[test]
-    fn smoke_shared_port_gone2() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        drop(rx);
-        let tx2 = tx.clone();
-        drop(tx);
-        assert!(tx2.send(1).is_err());
-    }
-
-    #[test]
-    fn port_gone_concurrent() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap();
-        });
-        while tx.send(1).is_ok() {}
-    }
-
-    #[test]
-    fn port_gone_concurrent_shared() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let tx2 = tx.clone();
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap();
-        });
-        while tx.send(1).is_ok() && tx2.send(1).is_ok() {}
-    }
-
-    #[test]
-    fn smoke_chan_gone() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        drop(tx);
-        assert!(rx.recv().is_err());
-    }
-
-    #[test]
-    fn smoke_chan_gone_shared() {
-        let (tx, rx) = sync_channel::<()>(0);
-        let tx2 = tx.clone();
-        drop(tx);
-        drop(tx2);
-        assert!(rx.recv().is_err());
-    }
-
-    #[test]
-    fn chan_gone_concurrent() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        thread::spawn(move || {
-            tx.send(1).unwrap();
-            tx.send(1).unwrap();
-        });
-        while rx.recv().is_ok() {}
-    }
-
-    #[test]
-    fn stress() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        thread::spawn(move || {
-            for _ in 0..10000 {
-                tx.send(1).unwrap();
-            }
-        });
-        for _ in 0..10000 {
-            assert_eq!(rx.recv().unwrap(), 1);
-        }
-    }
-
-    #[test]
-    fn stress_recv_timeout_two_threads() {
-        let (tx, rx) = sync_channel::<i32>(0);
-
-        thread::spawn(move || {
-            for _ in 0..10000 {
-                tx.send(1).unwrap();
-            }
-        });
-
-        let mut recv_count = 0;
-        loop {
-            match rx.recv_timeout(Duration::from_millis(1)) {
-                Ok(v) => {
-                    assert_eq!(v, 1);
-                    recv_count += 1;
-                }
-                Err(RecvTimeoutError::Timeout) => continue,
-                Err(RecvTimeoutError::Disconnected) => break,
-            }
-        }
-
-        assert_eq!(recv_count, 10000);
-    }
-
-    #[test]
-    fn stress_recv_timeout_shared() {
-        const AMT: u32 = 1000;
-        const NTHREADS: u32 = 8;
-        let (tx, rx) = sync_channel::<i32>(0);
-        let (dtx, drx) = sync_channel::<()>(0);
-
-        thread::spawn(move || {
-            let mut recv_count = 0;
-            loop {
-                match rx.recv_timeout(Duration::from_millis(10)) {
-                    Ok(v) => {
-                        assert_eq!(v, 1);
-                        recv_count += 1;
-                    }
-                    Err(RecvTimeoutError::Timeout) => continue,
-                    Err(RecvTimeoutError::Disconnected) => break,
-                }
-            }
-
-            assert_eq!(recv_count, AMT * NTHREADS);
-            assert!(rx.try_recv().is_err());
-
-            dtx.send(()).unwrap();
-        });
-
-        for _ in 0..NTHREADS {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                for _ in 0..AMT {
-                    tx.send(1).unwrap();
-                }
-            });
-        }
-
-        drop(tx);
-
-        drx.recv().unwrap();
-    }
-
-    #[test]
-    fn stress_shared() {
-        const AMT: u32 = 1000;
-        const NTHREADS: u32 = 8;
-        let (tx, rx) = sync_channel::<i32>(0);
-        let (dtx, drx) = sync_channel::<()>(0);
-
-        thread::spawn(move || {
-            for _ in 0..AMT * NTHREADS {
-                assert_eq!(rx.recv().unwrap(), 1);
-            }
-            match rx.try_recv() {
-                Ok(..) => panic!(),
-                _ => {}
-            }
-            dtx.send(()).unwrap();
-        });
-
-        for _ in 0..NTHREADS {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                for _ in 0..AMT {
-                    tx.send(1).unwrap();
-                }
-            });
-        }
-        drop(tx);
-        drx.recv().unwrap();
-    }
-
-    #[test]
-    fn oneshot_single_thread_close_port_first() {
-        // Simple test of closing without sending
-        let (_tx, rx) = sync_channel::<i32>(0);
-        drop(rx);
-    }
-
-    #[test]
-    fn oneshot_single_thread_close_chan_first() {
-        // Simple test of closing without sending
-        let (tx, _rx) = sync_channel::<i32>(0);
-        drop(tx);
-    }
-
-    #[test]
-    fn oneshot_single_thread_send_port_close() {
-        // Testing that the sender cleans up the payload if receiver is closed
-        let (tx, rx) = sync_channel::<Box<i32>>(0);
-        drop(rx);
-        assert!(tx.send(box 0).is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_recv_chan_close() {
-        // Receiving on a closed chan will panic
-        let res = thread::spawn(move || {
-            let (tx, rx) = sync_channel::<i32>(0);
-            drop(tx);
-            rx.recv().unwrap();
-        })
-        .join();
-        // What is our res?
-        assert!(res.is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_send_then_recv() {
-        let (tx, rx) = sync_channel::<Box<i32>>(1);
-        tx.send(box 10).unwrap();
-        assert!(*rx.recv().unwrap() == 10);
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_send_open() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        assert_eq!(tx.try_send(10), Ok(()));
-        assert!(rx.recv().unwrap() == 10);
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_send_closed() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        drop(rx);
-        assert_eq!(tx.try_send(10), Err(TrySendError::Disconnected(10)));
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_send_closed2() {
-        let (tx, _rx) = sync_channel::<i32>(0);
-        assert_eq!(tx.try_send(10), Err(TrySendError::Full(10)));
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_recv_open() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        tx.send(10).unwrap();
-        assert!(rx.recv() == Ok(10));
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_recv_closed() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        drop(tx);
-        assert!(rx.recv().is_err());
-    }
-
-    #[test]
-    fn oneshot_single_thread_try_recv_closed_with_data() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        tx.send(10).unwrap();
-        drop(tx);
-        assert_eq!(rx.try_recv(), Ok(10));
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
-    }
-
-    #[test]
-    fn oneshot_single_thread_peek_data() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
-        tx.send(10).unwrap();
-        assert_eq!(rx.try_recv(), Ok(10));
-    }
-
-    #[test]
-    fn oneshot_single_thread_peek_close() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        drop(tx);
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
-    }
-
-    #[test]
-    fn oneshot_single_thread_peek_open() {
-        let (_tx, rx) = sync_channel::<i32>(0);
-        assert_eq!(rx.try_recv(), Err(TryRecvError::Empty));
-    }
-
-    #[test]
-    fn oneshot_multi_task_recv_then_send() {
-        let (tx, rx) = sync_channel::<Box<i32>>(0);
-        let _t = thread::spawn(move || {
-            assert!(*rx.recv().unwrap() == 10);
-        });
-
-        tx.send(box 10).unwrap();
-    }
-
-    #[test]
-    fn oneshot_multi_task_recv_then_close() {
-        let (tx, rx) = sync_channel::<Box<i32>>(0);
-        let _t = thread::spawn(move || {
-            drop(tx);
-        });
-        let res = thread::spawn(move || {
-            assert!(*rx.recv().unwrap() == 10);
-        })
-        .join();
-        assert!(res.is_err());
-    }
-
-    #[test]
-    fn oneshot_multi_thread_close_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = sync_channel::<i32>(0);
-            let _t = thread::spawn(move || {
-                drop(rx);
-            });
-            drop(tx);
-        }
-    }
-
-    #[test]
-    fn oneshot_multi_thread_send_close_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = sync_channel::<i32>(0);
-            let _t = thread::spawn(move || {
-                drop(rx);
-            });
-            let _ = thread::spawn(move || {
-                tx.send(1).unwrap();
-            })
-            .join();
-        }
-    }
-
-    #[test]
-    fn oneshot_multi_thread_recv_close_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = sync_channel::<i32>(0);
-            let _t = thread::spawn(move || {
-                let res = thread::spawn(move || {
-                    rx.recv().unwrap();
-                })
-                .join();
-                assert!(res.is_err());
-            });
-            let _t = thread::spawn(move || {
-                thread::spawn(move || {
-                    drop(tx);
-                });
-            });
-        }
-    }
-
-    #[test]
-    fn oneshot_multi_thread_send_recv_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = sync_channel::<Box<i32>>(0);
-            let _t = thread::spawn(move || {
-                tx.send(box 10).unwrap();
-            });
-            assert!(*rx.recv().unwrap() == 10);
-        }
-    }
-
-    #[test]
-    fn stream_send_recv_stress() {
-        for _ in 0..stress_factor() {
-            let (tx, rx) = sync_channel::<Box<i32>>(0);
-
-            send(tx, 0);
-            recv(rx, 0);
-
-            fn send(tx: SyncSender<Box<i32>>, i: i32) {
-                if i == 10 {
-                    return;
-                }
-
-                thread::spawn(move || {
-                    tx.send(box i).unwrap();
-                    send(tx, i + 1);
-                });
-            }
-
-            fn recv(rx: Receiver<Box<i32>>, i: i32) {
-                if i == 10 {
-                    return;
-                }
-
-                thread::spawn(move || {
-                    assert!(*rx.recv().unwrap() == i);
-                    recv(rx, i + 1);
-                });
-            }
-        }
-    }
-
-    #[test]
-    fn recv_a_lot() {
-        // Regression test that we don't run out of stack in scheduler context
-        let (tx, rx) = sync_channel(10000);
-        for _ in 0..10000 {
-            tx.send(()).unwrap();
-        }
-        for _ in 0..10000 {
-            rx.recv().unwrap();
-        }
-    }
-
-    #[test]
-    fn shared_chan_stress() {
-        let (tx, rx) = sync_channel(0);
-        let total = stress_factor() + 100;
-        for _ in 0..total {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                tx.send(()).unwrap();
-            });
-        }
-
-        for _ in 0..total {
-            rx.recv().unwrap();
-        }
-    }
-
-    #[test]
-    fn test_nested_recv_iter() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let (total_tx, total_rx) = sync_channel::<i32>(0);
-
-        let _t = thread::spawn(move || {
-            let mut acc = 0;
-            for x in rx.iter() {
-                acc += x;
-            }
-            total_tx.send(acc).unwrap();
-        });
-
-        tx.send(3).unwrap();
-        tx.send(1).unwrap();
-        tx.send(2).unwrap();
-        drop(tx);
-        assert_eq!(total_rx.recv().unwrap(), 6);
-    }
-
-    #[test]
-    fn test_recv_iter_break() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let (count_tx, count_rx) = sync_channel(0);
-
-        let _t = thread::spawn(move || {
-            let mut count = 0;
-            for x in rx.iter() {
-                if count >= 3 {
-                    break;
-                } else {
-                    count += x;
-                }
-            }
-            count_tx.send(count).unwrap();
-        });
-
-        tx.send(2).unwrap();
-        tx.send(2).unwrap();
-        tx.send(2).unwrap();
-        let _ = tx.try_send(2);
-        drop(tx);
-        assert_eq!(count_rx.recv().unwrap(), 4);
-    }
-
-    #[test]
-    fn try_recv_states() {
-        let (tx1, rx1) = sync_channel::<i32>(1);
-        let (tx2, rx2) = sync_channel::<()>(1);
-        let (tx3, rx3) = sync_channel::<()>(1);
-        let _t = thread::spawn(move || {
-            rx2.recv().unwrap();
-            tx1.send(1).unwrap();
-            tx3.send(()).unwrap();
-            rx2.recv().unwrap();
-            drop(tx1);
-            tx3.send(()).unwrap();
-        });
-
-        assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
-        tx2.send(()).unwrap();
-        rx3.recv().unwrap();
-        assert_eq!(rx1.try_recv(), Ok(1));
-        assert_eq!(rx1.try_recv(), Err(TryRecvError::Empty));
-        tx2.send(()).unwrap();
-        rx3.recv().unwrap();
-        assert_eq!(rx1.try_recv(), Err(TryRecvError::Disconnected));
-    }
-
-    // This bug used to end up in a livelock inside of the Receiver destructor
-    // because the internal state of the Shared packet was corrupted
-    #[test]
-    fn destroy_upgraded_shared_port_when_sender_still_active() {
-        let (tx, rx) = sync_channel::<()>(0);
-        let (tx2, rx2) = sync_channel::<()>(0);
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap(); // wait on a oneshot
-            drop(rx); // destroy a shared
-            tx2.send(()).unwrap();
-        });
-        // make sure the other thread has gone to sleep
-        for _ in 0..5000 {
-            thread::yield_now();
-        }
-
-        // upgrade to a shared chan and send a message
-        let t = tx.clone();
-        drop(tx);
-        t.send(()).unwrap();
-
-        // wait for the child thread to exit before we exit
-        rx2.recv().unwrap();
-    }
-
-    #[test]
-    fn send1() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let _t = thread::spawn(move || {
-            rx.recv().unwrap();
-        });
-        assert_eq!(tx.send(1), Ok(()));
-    }
-
-    #[test]
-    fn send2() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let _t = thread::spawn(move || {
-            drop(rx);
-        });
-        assert!(tx.send(1).is_err());
-    }
-
-    #[test]
-    fn send3() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        assert_eq!(tx.send(1), Ok(()));
-        let _t = thread::spawn(move || {
-            drop(rx);
-        });
-        assert!(tx.send(1).is_err());
-    }
-
-    #[test]
-    fn send4() {
-        let (tx, rx) = sync_channel::<i32>(0);
-        let tx2 = tx.clone();
-        let (done, donerx) = channel();
-        let done2 = done.clone();
-        let _t = thread::spawn(move || {
-            assert!(tx.send(1).is_err());
-            done.send(()).unwrap();
-        });
-        let _t = thread::spawn(move || {
-            assert!(tx2.send(2).is_err());
-            done2.send(()).unwrap();
-        });
-        drop(rx);
-        donerx.recv().unwrap();
-        donerx.recv().unwrap();
-    }
-
-    #[test]
-    fn try_send1() {
-        let (tx, _rx) = sync_channel::<i32>(0);
-        assert_eq!(tx.try_send(1), Err(TrySendError::Full(1)));
-    }
-
-    #[test]
-    fn try_send2() {
-        let (tx, _rx) = sync_channel::<i32>(1);
-        assert_eq!(tx.try_send(1), Ok(()));
-        assert_eq!(tx.try_send(1), Err(TrySendError::Full(1)));
-    }
-
-    #[test]
-    fn try_send3() {
-        let (tx, rx) = sync_channel::<i32>(1);
-        assert_eq!(tx.try_send(1), Ok(()));
-        drop(rx);
-        assert_eq!(tx.try_send(1), Err(TrySendError::Disconnected(1)));
-    }
-
-    #[test]
-    fn issue_15761() {
-        fn repro() {
-            let (tx1, rx1) = sync_channel::<()>(3);
-            let (tx2, rx2) = sync_channel::<()>(3);
-
-            let _t = thread::spawn(move || {
-                rx1.recv().unwrap();
-                tx2.try_send(()).unwrap();
-            });
-
-            tx1.try_send(()).unwrap();
-            rx2.recv().unwrap();
-        }
-
-        for _ in 0..100 {
-            repro()
-        }
-    }
-}
diff --git a/src/libstd/sync/mpsc/mpsc_queue.rs b/src/libstd/sync/mpsc/mpsc_queue.rs
deleted file mode 100644
index 6e7a7be4430..00000000000
--- a/src/libstd/sync/mpsc/mpsc_queue.rs
+++ /dev/null
@@ -1,165 +0,0 @@
-//! A mostly lock-free multi-producer, single consumer queue.
-//!
-//! This module contains an implementation of a concurrent MPSC queue. This
-//! queue can be used to share data between threads, and is also used as the
-//! building block of channels in rust.
-//!
-//! Note that the current implementation of this queue has a caveat of the `pop`
-//! method, and see the method for more information about it. Due to this
-//! caveat, this queue may not be appropriate for all use-cases.
-
-// http://www.1024cores.net/home/lock-free-algorithms
-//                         /queues/non-intrusive-mpsc-node-based-queue
-
-pub use self::PopResult::*;
-
-use core::cell::UnsafeCell;
-use core::ptr;
-
-use crate::boxed::Box;
-use crate::sync::atomic::{AtomicPtr, Ordering};
-
-/// A result of the `pop` function.
-pub enum PopResult<T> {
-    /// Some data has been popped
-    Data(T),
-    /// The queue is empty
-    Empty,
-    /// The queue is in an inconsistent state. Popping data should succeed, but
-    /// some pushers have yet to make enough progress in order allow a pop to
-    /// succeed. It is recommended that a pop() occur "in the near future" in
-    /// order to see if the sender has made progress or not
-    Inconsistent,
-}
-
-struct Node<T> {
-    next: AtomicPtr<Node<T>>,
-    value: Option<T>,
-}
-
-/// The multi-producer single-consumer structure. This is not cloneable, but it
-/// may be safely shared so long as it is guaranteed that there is only one
-/// popper at a time (many pushers are allowed).
-pub struct Queue<T> {
-    head: AtomicPtr<Node<T>>,
-    tail: UnsafeCell<*mut Node<T>>,
-}
-
-unsafe impl<T: Send> Send for Queue<T> {}
-unsafe impl<T: Send> Sync for Queue<T> {}
-
-impl<T> Node<T> {
-    unsafe fn new(v: Option<T>) -> *mut Node<T> {
-        Box::into_raw(box Node { next: AtomicPtr::new(ptr::null_mut()), value: v })
-    }
-}
-
-impl<T> Queue<T> {
-    /// Creates a new queue that is safe to share among multiple producers and
-    /// one consumer.
-    pub fn new() -> Queue<T> {
-        let stub = unsafe { Node::new(None) };
-        Queue { head: AtomicPtr::new(stub), tail: UnsafeCell::new(stub) }
-    }
-
-    /// Pushes a new value onto this queue.
-    pub fn push(&self, t: T) {
-        unsafe {
-            let n = Node::new(Some(t));
-            let prev = self.head.swap(n, Ordering::AcqRel);
-            (*prev).next.store(n, Ordering::Release);
-        }
-    }
-
-    /// Pops some data from this queue.
-    ///
-    /// Note that the current implementation means that this function cannot
-    /// return `Option<T>`. It is possible for this queue to be in an
-    /// inconsistent state where many pushes have succeeded and completely
-    /// finished, but pops cannot return `Some(t)`. This inconsistent state
-    /// happens when a pusher is pre-empted at an inopportune moment.
-    ///
-    /// This inconsistent state means that this queue does indeed have data, but
-    /// it does not currently have access to it at this time.
-    pub fn pop(&self) -> PopResult<T> {
-        unsafe {
-            let tail = *self.tail.get();
-            let next = (*tail).next.load(Ordering::Acquire);
-
-            if !next.is_null() {
-                *self.tail.get() = next;
-                assert!((*tail).value.is_none());
-                assert!((*next).value.is_some());
-                let ret = (*next).value.take().unwrap();
-                let _: Box<Node<T>> = Box::from_raw(tail);
-                return Data(ret);
-            }
-
-            if self.head.load(Ordering::Acquire) == tail { Empty } else { Inconsistent }
-        }
-    }
-}
-
-impl<T> Drop for Queue<T> {
-    fn drop(&mut self) {
-        unsafe {
-            let mut cur = *self.tail.get();
-            while !cur.is_null() {
-                let next = (*cur).next.load(Ordering::Relaxed);
-                let _: Box<Node<T>> = Box::from_raw(cur);
-                cur = next;
-            }
-        }
-    }
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod tests {
-    use super::{Data, Empty, Inconsistent, Queue};
-    use crate::sync::mpsc::channel;
-    use crate::sync::Arc;
-    use crate::thread;
-
-    #[test]
-    fn test_full() {
-        let q: Queue<Box<_>> = Queue::new();
-        q.push(box 1);
-        q.push(box 2);
-    }
-
-    #[test]
-    fn test() {
-        let nthreads = 8;
-        let nmsgs = 1000;
-        let q = Queue::new();
-        match q.pop() {
-            Empty => {}
-            Inconsistent | Data(..) => panic!(),
-        }
-        let (tx, rx) = channel();
-        let q = Arc::new(q);
-
-        for _ in 0..nthreads {
-            let tx = tx.clone();
-            let q = q.clone();
-            thread::spawn(move || {
-                for i in 0..nmsgs {
-                    q.push(i);
-                }
-                tx.send(()).unwrap();
-            });
-        }
-
-        let mut i = 0;
-        while i < nthreads * nmsgs {
-            match q.pop() {
-                Empty | Inconsistent => {}
-                Data(_) => i += 1,
-            }
-        }
-        drop(tx);
-        for _ in 0..nthreads {
-            rx.recv().unwrap();
-        }
-    }
-}
diff --git a/src/libstd/sync/mpsc/oneshot.rs b/src/libstd/sync/mpsc/oneshot.rs
deleted file mode 100644
index 75f5621fa12..00000000000
--- a/src/libstd/sync/mpsc/oneshot.rs
+++ /dev/null
@@ -1,307 +0,0 @@
-/// Oneshot channels/ports
-///
-/// This is the initial flavor of channels/ports used for comm module. This is
-/// an optimization for the one-use case of a channel. The major optimization of
-/// this type is to have one and exactly one allocation when the chan/port pair
-/// is created.
-///
-/// Another possible optimization would be to not use an Arc box because
-/// in theory we know when the shared packet can be deallocated (no real need
-/// for the atomic reference counting), but I was having trouble how to destroy
-/// the data early in a drop of a Port.
-///
-/// # Implementation
-///
-/// Oneshots are implemented around one atomic usize variable. This variable
-/// indicates both the state of the port/chan but also contains any threads
-/// blocked on the port. All atomic operations happen on this one word.
-///
-/// In order to upgrade a oneshot channel, an upgrade is considered a disconnect
-/// on behalf of the channel side of things (it can be mentally thought of as
-/// consuming the port). This upgrade is then also stored in the shared packet.
-/// The one caveat to consider is that when a port sees a disconnected channel
-/// it must check for data because there is no "data plus upgrade" state.
-pub use self::Failure::*;
-use self::MyUpgrade::*;
-pub use self::UpgradeResult::*;
-
-use crate::cell::UnsafeCell;
-use crate::ptr;
-use crate::sync::atomic::{AtomicUsize, Ordering};
-use crate::sync::mpsc::blocking::{self, SignalToken};
-use crate::sync::mpsc::Receiver;
-use crate::time::Instant;
-
-// Various states you can find a port in.
-const EMPTY: usize = 0; // initial state: no data, no blocked receiver
-const DATA: usize = 1; // data ready for receiver to take
-const DISCONNECTED: usize = 2; // channel is disconnected OR upgraded
-// Any other value represents a pointer to a SignalToken value. The
-// protocol ensures that when the state moves *to* a pointer,
-// ownership of the token is given to the packet, and when the state
-// moves *from* a pointer, ownership of the token is transferred to
-// whoever changed the state.
-
-pub struct Packet<T> {
-    // Internal state of the chan/port pair (stores the blocked thread as well)
-    state: AtomicUsize,
-    // One-shot data slot location
-    data: UnsafeCell<Option<T>>,
-    // when used for the second time, a oneshot channel must be upgraded, and
-    // this contains the slot for the upgrade
-    upgrade: UnsafeCell<MyUpgrade<T>>,
-}
-
-pub enum Failure<T> {
-    Empty,
-    Disconnected,
-    Upgraded(Receiver<T>),
-}
-
-pub enum UpgradeResult {
-    UpSuccess,
-    UpDisconnected,
-    UpWoke(SignalToken),
-}
-
-enum MyUpgrade<T> {
-    NothingSent,
-    SendUsed,
-    GoUp(Receiver<T>),
-}
-
-impl<T> Packet<T> {
-    pub fn new() -> Packet<T> {
-        Packet {
-            data: UnsafeCell::new(None),
-            upgrade: UnsafeCell::new(NothingSent),
-            state: AtomicUsize::new(EMPTY),
-        }
-    }
-
-    pub fn send(&self, t: T) -> Result<(), T> {
-        unsafe {
-            // Sanity check
-            match *self.upgrade.get() {
-                NothingSent => {}
-                _ => panic!("sending on a oneshot that's already sent on "),
-            }
-            assert!((*self.data.get()).is_none());
-            ptr::write(self.data.get(), Some(t));
-            ptr::write(self.upgrade.get(), SendUsed);
-
-            match self.state.swap(DATA, Ordering::SeqCst) {
-                // Sent the data, no one was waiting
-                EMPTY => Ok(()),
-
-                // Couldn't send the data, the port hung up first. Return the data
-                // back up the stack.
-                DISCONNECTED => {
-                    self.state.swap(DISCONNECTED, Ordering::SeqCst);
-                    ptr::write(self.upgrade.get(), NothingSent);
-                    Err((&mut *self.data.get()).take().unwrap())
-                }
-
-                // Not possible, these are one-use channels
-                DATA => unreachable!(),
-
-                // There is a thread waiting on the other end. We leave the 'DATA'
-                // state inside so it'll pick it up on the other end.
-                ptr => {
-                    SignalToken::cast_from_usize(ptr).signal();
-                    Ok(())
-                }
-            }
-        }
-    }
-
-    // Just tests whether this channel has been sent on or not, this is only
-    // safe to use from the sender.
-    pub fn sent(&self) -> bool {
-        unsafe { !matches!(*self.upgrade.get(), NothingSent) }
-    }
-
-    pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure<T>> {
-        // Attempt to not block the thread (it's a little expensive). If it looks
-        // like we're not empty, then immediately go through to `try_recv`.
-        if self.state.load(Ordering::SeqCst) == EMPTY {
-            let (wait_token, signal_token) = blocking::tokens();
-            let ptr = unsafe { signal_token.cast_to_usize() };
-
-            // race with senders to enter the blocking state
-            if self.state.compare_and_swap(EMPTY, ptr, Ordering::SeqCst) == EMPTY {
-                if let Some(deadline) = deadline {
-                    let timed_out = !wait_token.wait_max_until(deadline);
-                    // Try to reset the state
-                    if timed_out {
-                        self.abort_selection().map_err(Upgraded)?;
-                    }
-                } else {
-                    wait_token.wait();
-                    debug_assert!(self.state.load(Ordering::SeqCst) != EMPTY);
-                }
-            } else {
-                // drop the signal token, since we never blocked
-                drop(unsafe { SignalToken::cast_from_usize(ptr) });
-            }
-        }
-
-        self.try_recv()
-    }
-
-    pub fn try_recv(&self) -> Result<T, Failure<T>> {
-        unsafe {
-            match self.state.load(Ordering::SeqCst) {
-                EMPTY => Err(Empty),
-
-                // We saw some data on the channel, but the channel can be used
-                // again to send us an upgrade. As a result, we need to re-insert
-                // into the channel that there's no data available (otherwise we'll
-                // just see DATA next time). This is done as a cmpxchg because if
-                // the state changes under our feet we'd rather just see that state
-                // change.
-                DATA => {
-                    self.state.compare_and_swap(DATA, EMPTY, Ordering::SeqCst);
-                    match (&mut *self.data.get()).take() {
-                        Some(data) => Ok(data),
-                        None => unreachable!(),
-                    }
-                }
-
-                // There's no guarantee that we receive before an upgrade happens,
-                // and an upgrade flags the channel as disconnected, so when we see
-                // this we first need to check if there's data available and *then*
-                // we go through and process the upgrade.
-                DISCONNECTED => match (&mut *self.data.get()).take() {
-                    Some(data) => Ok(data),
-                    None => match ptr::replace(self.upgrade.get(), SendUsed) {
-                        SendUsed | NothingSent => Err(Disconnected),
-                        GoUp(upgrade) => Err(Upgraded(upgrade)),
-                    },
-                },
-
-                // We are the sole receiver; there cannot be a blocking
-                // receiver already.
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    // Returns whether the upgrade was completed. If the upgrade wasn't
-    // completed, then the port couldn't get sent to the other half (it will
-    // never receive it).
-    pub fn upgrade(&self, up: Receiver<T>) -> UpgradeResult {
-        unsafe {
-            let prev = match *self.upgrade.get() {
-                NothingSent => NothingSent,
-                SendUsed => SendUsed,
-                _ => panic!("upgrading again"),
-            };
-            ptr::write(self.upgrade.get(), GoUp(up));
-
-            match self.state.swap(DISCONNECTED, Ordering::SeqCst) {
-                // If the channel is empty or has data on it, then we're good to go.
-                // Senders will check the data before the upgrade (in case we
-                // plastered over the DATA state).
-                DATA | EMPTY => UpSuccess,
-
-                // If the other end is already disconnected, then we failed the
-                // upgrade. Be sure to trash the port we were given.
-                DISCONNECTED => {
-                    ptr::replace(self.upgrade.get(), prev);
-                    UpDisconnected
-                }
-
-                // If someone's waiting, we gotta wake them up
-                ptr => UpWoke(SignalToken::cast_from_usize(ptr)),
-            }
-        }
-    }
-
-    pub fn drop_chan(&self) {
-        match self.state.swap(DISCONNECTED, Ordering::SeqCst) {
-            DATA | DISCONNECTED | EMPTY => {}
-
-            // If someone's waiting, we gotta wake them up
-            ptr => unsafe {
-                SignalToken::cast_from_usize(ptr).signal();
-            },
-        }
-    }
-
-    pub fn drop_port(&self) {
-        match self.state.swap(DISCONNECTED, Ordering::SeqCst) {
-            // An empty channel has nothing to do, and a remotely disconnected
-            // channel also has nothing to do b/c we're about to run the drop
-            // glue
-            DISCONNECTED | EMPTY => {}
-
-            // There's data on the channel, so make sure we destroy it promptly.
-            // This is why not using an arc is a little difficult (need the box
-            // to stay valid while we take the data).
-            DATA => unsafe {
-                (&mut *self.data.get()).take().unwrap();
-            },
-
-            // We're the only ones that can block on this port
-            _ => unreachable!(),
-        }
-    }
-
-    ////////////////////////////////////////////////////////////////////////////
-    // select implementation
-    ////////////////////////////////////////////////////////////////////////////
-
-    // Remove a previous selecting thread from this port. This ensures that the
-    // blocked thread will no longer be visible to any other threads.
-    //
-    // The return value indicates whether there's data on this port.
-    pub fn abort_selection(&self) -> Result<bool, Receiver<T>> {
-        let state = match self.state.load(Ordering::SeqCst) {
-            // Each of these states means that no further activity will happen
-            // with regard to abortion selection
-            s @ (EMPTY | DATA | DISCONNECTED) => s,
-
-            // If we've got a blocked thread, then use an atomic to gain ownership
-            // of it (may fail)
-            ptr => self.state.compare_and_swap(ptr, EMPTY, Ordering::SeqCst),
-        };
-
-        // Now that we've got ownership of our state, figure out what to do
-        // about it.
-        match state {
-            EMPTY => unreachable!(),
-            // our thread used for select was stolen
-            DATA => Ok(true),
-
-            // If the other end has hung up, then we have complete ownership
-            // of the port. First, check if there was data waiting for us. This
-            // is possible if the other end sent something and then hung up.
-            //
-            // We then need to check to see if there was an upgrade requested,
-            // and if so, the upgraded port needs to have its selection aborted.
-            DISCONNECTED => unsafe {
-                if (*self.data.get()).is_some() {
-                    Ok(true)
-                } else {
-                    match ptr::replace(self.upgrade.get(), SendUsed) {
-                        GoUp(port) => Err(port),
-                        _ => Ok(true),
-                    }
-                }
-            },
-
-            // We woke ourselves up from select.
-            ptr => unsafe {
-                drop(SignalToken::cast_from_usize(ptr));
-                Ok(false)
-            },
-        }
-    }
-}
-
-impl<T> Drop for Packet<T> {
-    fn drop(&mut self) {
-        assert_eq!(self.state.load(Ordering::SeqCst), DISCONNECTED);
-    }
-}
diff --git a/src/libstd/sync/mpsc/shared.rs b/src/libstd/sync/mpsc/shared.rs
deleted file mode 100644
index 898654f21f2..00000000000
--- a/src/libstd/sync/mpsc/shared.rs
+++ /dev/null
@@ -1,489 +0,0 @@
-/// Shared channels.
-///
-/// This is the flavor of channels which are not necessarily optimized for any
-/// particular use case, but are the most general in how they are used. Shared
-/// channels are cloneable allowing for multiple senders.
-///
-/// High level implementation details can be found in the comment of the parent
-/// module. You'll also note that the implementation of the shared and stream
-/// channels are quite similar, and this is no coincidence!
-pub use self::Failure::*;
-use self::StartResult::*;
-
-use core::cmp;
-use core::intrinsics::abort;
-
-use crate::cell::UnsafeCell;
-use crate::ptr;
-use crate::sync::atomic::{AtomicBool, AtomicIsize, AtomicUsize, Ordering};
-use crate::sync::mpsc::blocking::{self, SignalToken};
-use crate::sync::mpsc::mpsc_queue as mpsc;
-use crate::sync::{Mutex, MutexGuard};
-use crate::thread;
-use crate::time::Instant;
-
-const DISCONNECTED: isize = isize::MIN;
-const FUDGE: isize = 1024;
-const MAX_REFCOUNT: usize = (isize::MAX) as usize;
-#[cfg(test)]
-const MAX_STEALS: isize = 5;
-#[cfg(not(test))]
-const MAX_STEALS: isize = 1 << 20;
-
-pub struct Packet<T> {
-    queue: mpsc::Queue<T>,
-    cnt: AtomicIsize,          // How many items are on this channel
-    steals: UnsafeCell<isize>, // How many times has a port received without blocking?
-    to_wake: AtomicUsize,      // SignalToken for wake up
-
-    // The number of channels which are currently using this packet.
-    channels: AtomicUsize,
-
-    // See the discussion in Port::drop and the channel send methods for what
-    // these are used for
-    port_dropped: AtomicBool,
-    sender_drain: AtomicIsize,
-
-    // this lock protects various portions of this implementation during
-    // select()
-    select_lock: Mutex<()>,
-}
-
-pub enum Failure {
-    Empty,
-    Disconnected,
-}
-
-#[derive(PartialEq, Eq)]
-enum StartResult {
-    Installed,
-    Abort,
-}
-
-impl<T> Packet<T> {
-    // Creation of a packet *must* be followed by a call to postinit_lock
-    // and later by inherit_blocker
-    pub fn new() -> Packet<T> {
-        Packet {
-            queue: mpsc::Queue::new(),
-            cnt: AtomicIsize::new(0),
-            steals: UnsafeCell::new(0),
-            to_wake: AtomicUsize::new(0),
-            channels: AtomicUsize::new(2),
-            port_dropped: AtomicBool::new(false),
-            sender_drain: AtomicIsize::new(0),
-            select_lock: Mutex::new(()),
-        }
-    }
-
-    // This function should be used after newly created Packet
-    // was wrapped with an Arc
-    // In other case mutex data will be duplicated while cloning
-    // and that could cause problems on platforms where it is
-    // represented by opaque data structure
-    pub fn postinit_lock(&self) -> MutexGuard<'_, ()> {
-        self.select_lock.lock().unwrap()
-    }
-
-    // This function is used at the creation of a shared packet to inherit a
-    // previously blocked thread. This is done to prevent spurious wakeups of
-    // threads in select().
-    //
-    // This can only be called at channel-creation time
-    pub fn inherit_blocker(&self, token: Option<SignalToken>, guard: MutexGuard<'_, ()>) {
-        if let Some(token) = token {
-            assert_eq!(self.cnt.load(Ordering::SeqCst), 0);
-            assert_eq!(self.to_wake.load(Ordering::SeqCst), 0);
-            self.to_wake.store(unsafe { token.cast_to_usize() }, Ordering::SeqCst);
-            self.cnt.store(-1, Ordering::SeqCst);
-
-            // This store is a little sketchy. What's happening here is that
-            // we're transferring a blocker from a oneshot or stream channel to
-            // this shared channel. In doing so, we never spuriously wake them
-            // up and rather only wake them up at the appropriate time. This
-            // implementation of shared channels assumes that any blocking
-            // recv() will undo the increment of steals performed in try_recv()
-            // once the recv is complete.  This thread that we're inheriting,
-            // however, is not in the middle of recv. Hence, the first time we
-            // wake them up, they're going to wake up from their old port, move
-            // on to the upgraded port, and then call the block recv() function.
-            //
-            // When calling this function, they'll find there's data immediately
-            // available, counting it as a steal. This in fact wasn't a steal
-            // because we appropriately blocked them waiting for data.
-            //
-            // To offset this bad increment, we initially set the steal count to
-            // -1. You'll find some special code in abort_selection() as well to
-            // ensure that this -1 steal count doesn't escape too far.
-            unsafe {
-                *self.steals.get() = -1;
-            }
-        }
-
-        // When the shared packet is constructed, we grabbed this lock. The
-        // purpose of this lock is to ensure that abort_selection() doesn't
-        // interfere with this method. After we unlock this lock, we're
-        // signifying that we're done modifying self.cnt and self.to_wake and
-        // the port is ready for the world to continue using it.
-        drop(guard);
-    }
-
-    pub fn send(&self, t: T) -> Result<(), T> {
-        // See Port::drop for what's going on
-        if self.port_dropped.load(Ordering::SeqCst) {
-            return Err(t);
-        }
-
-        // Note that the multiple sender case is a little trickier
-        // semantically than the single sender case. The logic for
-        // incrementing is "add and if disconnected store disconnected".
-        // This could end up leading some senders to believe that there
-        // wasn't a disconnect if in fact there was a disconnect. This means
-        // that while one thread is attempting to re-store the disconnected
-        // states, other threads could walk through merrily incrementing
-        // this very-negative disconnected count. To prevent senders from
-        // spuriously attempting to send when the channels is actually
-        // disconnected, the count has a ranged check here.
-        //
-        // This is also done for another reason. Remember that the return
-        // value of this function is:
-        //
-        //  `true` == the data *may* be received, this essentially has no
-        //            meaning
-        //  `false` == the data will *never* be received, this has a lot of
-        //             meaning
-        //
-        // In the SPSC case, we have a check of 'queue.is_empty()' to see
-        // whether the data was actually received, but this same condition
-        // means nothing in a multi-producer context. As a result, this
-        // preflight check serves as the definitive "this will never be
-        // received". Once we get beyond this check, we have permanently
-        // entered the realm of "this may be received"
-        if self.cnt.load(Ordering::SeqCst) < DISCONNECTED + FUDGE {
-            return Err(t);
-        }
-
-        self.queue.push(t);
-        match self.cnt.fetch_add(1, Ordering::SeqCst) {
-            -1 => {
-                self.take_to_wake().signal();
-            }
-
-            // In this case, we have possibly failed to send our data, and
-            // we need to consider re-popping the data in order to fully
-            // destroy it. We must arbitrate among the multiple senders,
-            // however, because the queues that we're using are
-            // single-consumer queues. In order to do this, all exiting
-            // pushers will use an atomic count in order to count those
-            // flowing through. Pushers who see 0 are required to drain as
-            // much as possible, and then can only exit when they are the
-            // only pusher (otherwise they must try again).
-            n if n < DISCONNECTED + FUDGE => {
-                // see the comment in 'try' for a shared channel for why this
-                // window of "not disconnected" is ok.
-                self.cnt.store(DISCONNECTED, Ordering::SeqCst);
-
-                if self.sender_drain.fetch_add(1, Ordering::SeqCst) == 0 {
-                    loop {
-                        // drain the queue, for info on the thread yield see the
-                        // discussion in try_recv
-                        loop {
-                            match self.queue.pop() {
-                                mpsc::Data(..) => {}
-                                mpsc::Empty => break,
-                                mpsc::Inconsistent => thread::yield_now(),
-                            }
-                        }
-                        // maybe we're done, if we're not the last ones
-                        // here, then we need to go try again.
-                        if self.sender_drain.fetch_sub(1, Ordering::SeqCst) == 1 {
-                            break;
-                        }
-                    }
-
-                    // At this point, there may still be data on the queue,
-                    // but only if the count hasn't been incremented and
-                    // some other sender hasn't finished pushing data just
-                    // yet. That sender in question will drain its own data.
-                }
-            }
-
-            // Can't make any assumptions about this case like in the SPSC case.
-            _ => {}
-        }
-
-        Ok(())
-    }
-
-    pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure> {
-        // This code is essentially the exact same as that found in the stream
-        // case (see stream.rs)
-        match self.try_recv() {
-            Err(Empty) => {}
-            data => return data,
-        }
-
-        let (wait_token, signal_token) = blocking::tokens();
-        if self.decrement(signal_token) == Installed {
-            if let Some(deadline) = deadline {
-                let timed_out = !wait_token.wait_max_until(deadline);
-                if timed_out {
-                    self.abort_selection(false);
-                }
-            } else {
-                wait_token.wait();
-            }
-        }
-
-        match self.try_recv() {
-            data @ Ok(..) => unsafe {
-                *self.steals.get() -= 1;
-                data
-            },
-            data => data,
-        }
-    }
-
-    // Essentially the exact same thing as the stream decrement function.
-    // Returns true if blocking should proceed.
-    fn decrement(&self, token: SignalToken) -> StartResult {
-        unsafe {
-            assert_eq!(self.to_wake.load(Ordering::SeqCst), 0);
-            let ptr = token.cast_to_usize();
-            self.to_wake.store(ptr, Ordering::SeqCst);
-
-            let steals = ptr::replace(self.steals.get(), 0);
-
-            match self.cnt.fetch_sub(1 + steals, Ordering::SeqCst) {
-                DISCONNECTED => {
-                    self.cnt.store(DISCONNECTED, Ordering::SeqCst);
-                }
-                // If we factor in our steals and notice that the channel has no
-                // data, we successfully sleep
-                n => {
-                    assert!(n >= 0);
-                    if n - steals <= 0 {
-                        return Installed;
-                    }
-                }
-            }
-
-            self.to_wake.store(0, Ordering::SeqCst);
-            drop(SignalToken::cast_from_usize(ptr));
-            Abort
-        }
-    }
-
-    pub fn try_recv(&self) -> Result<T, Failure> {
-        let ret = match self.queue.pop() {
-            mpsc::Data(t) => Some(t),
-            mpsc::Empty => None,
-
-            // This is a bit of an interesting case. The channel is reported as
-            // having data available, but our pop() has failed due to the queue
-            // being in an inconsistent state.  This means that there is some
-            // pusher somewhere which has yet to complete, but we are guaranteed
-            // that a pop will eventually succeed. In this case, we spin in a
-            // yield loop because the remote sender should finish their enqueue
-            // operation "very quickly".
-            //
-            // Avoiding this yield loop would require a different queue
-            // abstraction which provides the guarantee that after M pushes have
-            // succeeded, at least M pops will succeed. The current queues
-            // guarantee that if there are N active pushes, you can pop N times
-            // once all N have finished.
-            mpsc::Inconsistent => {
-                let data;
-                loop {
-                    thread::yield_now();
-                    match self.queue.pop() {
-                        mpsc::Data(t) => {
-                            data = t;
-                            break;
-                        }
-                        mpsc::Empty => panic!("inconsistent => empty"),
-                        mpsc::Inconsistent => {}
-                    }
-                }
-                Some(data)
-            }
-        };
-        match ret {
-            // See the discussion in the stream implementation for why we
-            // might decrement steals.
-            Some(data) => unsafe {
-                if *self.steals.get() > MAX_STEALS {
-                    match self.cnt.swap(0, Ordering::SeqCst) {
-                        DISCONNECTED => {
-                            self.cnt.store(DISCONNECTED, Ordering::SeqCst);
-                        }
-                        n => {
-                            let m = cmp::min(n, *self.steals.get());
-                            *self.steals.get() -= m;
-                            self.bump(n - m);
-                        }
-                    }
-                    assert!(*self.steals.get() >= 0);
-                }
-                *self.steals.get() += 1;
-                Ok(data)
-            },
-
-            // See the discussion in the stream implementation for why we try
-            // again.
-            None => {
-                match self.cnt.load(Ordering::SeqCst) {
-                    n if n != DISCONNECTED => Err(Empty),
-                    _ => {
-                        match self.queue.pop() {
-                            mpsc::Data(t) => Ok(t),
-                            mpsc::Empty => Err(Disconnected),
-                            // with no senders, an inconsistency is impossible.
-                            mpsc::Inconsistent => unreachable!(),
-                        }
-                    }
-                }
-            }
-        }
-    }
-
-    // Prepares this shared packet for a channel clone, essentially just bumping
-    // a refcount.
-    pub fn clone_chan(&self) {
-        let old_count = self.channels.fetch_add(1, Ordering::SeqCst);
-
-        // See comments on Arc::clone() on why we do this (for `mem::forget`).
-        if old_count > MAX_REFCOUNT {
-            abort();
-        }
-    }
-
-    // Decrement the reference count on a channel. This is called whenever a
-    // Chan is dropped and may end up waking up a receiver. It's the receiver's
-    // responsibility on the other end to figure out that we've disconnected.
-    pub fn drop_chan(&self) {
-        match self.channels.fetch_sub(1, Ordering::SeqCst) {
-            1 => {}
-            n if n > 1 => return,
-            n => panic!("bad number of channels left {}", n),
-        }
-
-        match self.cnt.swap(DISCONNECTED, Ordering::SeqCst) {
-            -1 => {
-                self.take_to_wake().signal();
-            }
-            DISCONNECTED => {}
-            n => {
-                assert!(n >= 0);
-            }
-        }
-    }
-
-    // See the long discussion inside of stream.rs for why the queue is drained,
-    // and why it is done in this fashion.
-    pub fn drop_port(&self) {
-        self.port_dropped.store(true, Ordering::SeqCst);
-        let mut steals = unsafe { *self.steals.get() };
-        while {
-            let cnt = self.cnt.compare_and_swap(steals, DISCONNECTED, Ordering::SeqCst);
-            cnt != DISCONNECTED && cnt != steals
-        } {
-            // See the discussion in 'try_recv' for why we yield
-            // control of this thread.
-            loop {
-                match self.queue.pop() {
-                    mpsc::Data(..) => {
-                        steals += 1;
-                    }
-                    mpsc::Empty | mpsc::Inconsistent => break,
-                }
-            }
-        }
-    }
-
-    // Consumes ownership of the 'to_wake' field.
-    fn take_to_wake(&self) -> SignalToken {
-        let ptr = self.to_wake.load(Ordering::SeqCst);
-        self.to_wake.store(0, Ordering::SeqCst);
-        assert!(ptr != 0);
-        unsafe { SignalToken::cast_from_usize(ptr) }
-    }
-
-    ////////////////////////////////////////////////////////////////////////////
-    // select implementation
-    ////////////////////////////////////////////////////////////////////////////
-
-    // increment the count on the channel (used for selection)
-    fn bump(&self, amt: isize) -> isize {
-        match self.cnt.fetch_add(amt, Ordering::SeqCst) {
-            DISCONNECTED => {
-                self.cnt.store(DISCONNECTED, Ordering::SeqCst);
-                DISCONNECTED
-            }
-            n => n,
-        }
-    }
-
-    // Cancels a previous thread waiting on this port, returning whether there's
-    // data on the port.
-    //
-    // This is similar to the stream implementation (hence fewer comments), but
-    // uses a different value for the "steals" variable.
-    pub fn abort_selection(&self, _was_upgrade: bool) -> bool {
-        // Before we do anything else, we bounce on this lock. The reason for
-        // doing this is to ensure that any upgrade-in-progress is gone and
-        // done with. Without this bounce, we can race with inherit_blocker
-        // about looking at and dealing with to_wake. Once we have acquired the
-        // lock, we are guaranteed that inherit_blocker is done.
-        {
-            let _guard = self.select_lock.lock().unwrap();
-        }
-
-        // Like the stream implementation, we want to make sure that the count
-        // on the channel goes non-negative. We don't know how negative the
-        // stream currently is, so instead of using a steal value of 1, we load
-        // the channel count and figure out what we should do to make it
-        // positive.
-        let steals = {
-            let cnt = self.cnt.load(Ordering::SeqCst);
-            if cnt < 0 && cnt != DISCONNECTED { -cnt } else { 0 }
-        };
-        let prev = self.bump(steals + 1);
-
-        if prev == DISCONNECTED {
-            assert_eq!(self.to_wake.load(Ordering::SeqCst), 0);
-            true
-        } else {
-            let cur = prev + steals + 1;
-            assert!(cur >= 0);
-            if prev < 0 {
-                drop(self.take_to_wake());
-            } else {
-                while self.to_wake.load(Ordering::SeqCst) != 0 {
-                    thread::yield_now();
-                }
-            }
-            unsafe {
-                // if the number of steals is -1, it was the pre-emptive -1 steal
-                // count from when we inherited a blocker. This is fine because
-                // we're just going to overwrite it with a real value.
-                let old = self.steals.get();
-                assert!(*old == 0 || *old == -1);
-                *old = steals;
-                prev >= 0
-            }
-        }
-    }
-}
-
-impl<T> Drop for Packet<T> {
-    fn drop(&mut self) {
-        // Note that this load is not only an assert for correctness about
-        // disconnection, but also a proper fence before the read of
-        // `to_wake`, so this assert cannot be removed with also removing
-        // the `to_wake` assert.
-        assert_eq!(self.cnt.load(Ordering::SeqCst), DISCONNECTED);
-        assert_eq!(self.to_wake.load(Ordering::SeqCst), 0);
-        assert_eq!(self.channels.load(Ordering::SeqCst), 0);
-    }
-}
diff --git a/src/libstd/sync/mpsc/spsc_queue.rs b/src/libstd/sync/mpsc/spsc_queue.rs
deleted file mode 100644
index 0274268f69f..00000000000
--- a/src/libstd/sync/mpsc/spsc_queue.rs
+++ /dev/null
@@ -1,338 +0,0 @@
-//! A single-producer single-consumer concurrent queue
-//!
-//! This module contains the implementation of an SPSC queue which can be used
-//! concurrently between two threads. This data structure is safe to use and
-//! enforces the semantics that there is one pusher and one popper.
-
-// http://www.1024cores.net/home/lock-free-algorithms/queues/unbounded-spsc-queue
-
-use core::cell::UnsafeCell;
-use core::ptr;
-
-use crate::boxed::Box;
-use crate::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
-
-use super::cache_aligned::CacheAligned;
-
-// Node within the linked list queue of messages to send
-struct Node<T> {
-    // FIXME: this could be an uninitialized T if we're careful enough, and
-    //      that would reduce memory usage (and be a bit faster).
-    //      is it worth it?
-    value: Option<T>,         // nullable for re-use of nodes
-    cached: bool,             // This node goes into the node cache
-    next: AtomicPtr<Node<T>>, // next node in the queue
-}
-
-/// The single-producer single-consumer queue. This structure is not cloneable,
-/// but it can be safely shared in an Arc if it is guaranteed that there
-/// is only one popper and one pusher touching the queue at any one point in
-/// time.
-pub struct Queue<T, ProducerAddition = (), ConsumerAddition = ()> {
-    // consumer fields
-    consumer: CacheAligned<Consumer<T, ConsumerAddition>>,
-
-    // producer fields
-    producer: CacheAligned<Producer<T, ProducerAddition>>,
-}
-
-struct Consumer<T, Addition> {
-    tail: UnsafeCell<*mut Node<T>>, // where to pop from
-    tail_prev: AtomicPtr<Node<T>>,  // where to pop from
-    cache_bound: usize,             // maximum cache size
-    cached_nodes: AtomicUsize,      // number of nodes marked as cacheable
-    addition: Addition,
-}
-
-struct Producer<T, Addition> {
-    head: UnsafeCell<*mut Node<T>>,      // where to push to
-    first: UnsafeCell<*mut Node<T>>,     // where to get new nodes from
-    tail_copy: UnsafeCell<*mut Node<T>>, // between first/tail
-    addition: Addition,
-}
-
-unsafe impl<T: Send, P: Send + Sync, C: Send + Sync> Send for Queue<T, P, C> {}
-
-unsafe impl<T: Send, P: Send + Sync, C: Send + Sync> Sync for Queue<T, P, C> {}
-
-impl<T> Node<T> {
-    fn new() -> *mut Node<T> {
-        Box::into_raw(box Node {
-            value: None,
-            cached: false,
-            next: AtomicPtr::new(ptr::null_mut::<Node<T>>()),
-        })
-    }
-}
-
-impl<T, ProducerAddition, ConsumerAddition> Queue<T, ProducerAddition, ConsumerAddition> {
-    /// Creates a new queue. With given additional elements in the producer and
-    /// consumer portions of the queue.
-    ///
-    /// Due to the performance implications of cache-contention,
-    /// we wish to keep fields used mainly by the producer on a separate cache
-    /// line than those used by the consumer.
-    /// Since cache lines are usually 64 bytes, it is unreasonably expensive to
-    /// allocate one for small fields, so we allow users to insert additional
-    /// fields into the cache lines already allocated by this for the producer
-    /// and consumer.
-    ///
-    /// This is unsafe as the type system doesn't enforce a single
-    /// consumer-producer relationship. It also allows the consumer to `pop`
-    /// items while there is a `peek` active due to all methods having a
-    /// non-mutable receiver.
-    ///
-    /// # Arguments
-    ///
-    ///   * `bound` - This queue implementation is implemented with a linked
-    ///               list, and this means that a push is always a malloc. In
-    ///               order to amortize this cost, an internal cache of nodes is
-    ///               maintained to prevent a malloc from always being
-    ///               necessary. This bound is the limit on the size of the
-    ///               cache (if desired). If the value is 0, then the cache has
-    ///               no bound. Otherwise, the cache will never grow larger than
-    ///               `bound` (although the queue itself could be much larger.
-    pub unsafe fn with_additions(
-        bound: usize,
-        producer_addition: ProducerAddition,
-        consumer_addition: ConsumerAddition,
-    ) -> Self {
-        let n1 = Node::new();
-        let n2 = Node::new();
-        (*n1).next.store(n2, Ordering::Relaxed);
-        Queue {
-            consumer: CacheAligned::new(Consumer {
-                tail: UnsafeCell::new(n2),
-                tail_prev: AtomicPtr::new(n1),
-                cache_bound: bound,
-                cached_nodes: AtomicUsize::new(0),
-                addition: consumer_addition,
-            }),
-            producer: CacheAligned::new(Producer {
-                head: UnsafeCell::new(n2),
-                first: UnsafeCell::new(n1),
-                tail_copy: UnsafeCell::new(n1),
-                addition: producer_addition,
-            }),
-        }
-    }
-
-    /// Pushes a new value onto this queue. Note that to use this function
-    /// safely, it must be externally guaranteed that there is only one pusher.
-    pub fn push(&self, t: T) {
-        unsafe {
-            // Acquire a node (which either uses a cached one or allocates a new
-            // one), and then append this to the 'head' node.
-            let n = self.alloc();
-            assert!((*n).value.is_none());
-            (*n).value = Some(t);
-            (*n).next.store(ptr::null_mut(), Ordering::Relaxed);
-            (**self.producer.head.get()).next.store(n, Ordering::Release);
-            *(&self.producer.head).get() = n;
-        }
-    }
-
-    unsafe fn alloc(&self) -> *mut Node<T> {
-        // First try to see if we can consume the 'first' node for our uses.
-        if *self.producer.first.get() != *self.producer.tail_copy.get() {
-            let ret = *self.producer.first.get();
-            *self.producer.0.first.get() = (*ret).next.load(Ordering::Relaxed);
-            return ret;
-        }
-        // If the above fails, then update our copy of the tail and try
-        // again.
-        *self.producer.0.tail_copy.get() = self.consumer.tail_prev.load(Ordering::Acquire);
-        if *self.producer.first.get() != *self.producer.tail_copy.get() {
-            let ret = *self.producer.first.get();
-            *self.producer.0.first.get() = (*ret).next.load(Ordering::Relaxed);
-            return ret;
-        }
-        // If all of that fails, then we have to allocate a new node
-        // (there's nothing in the node cache).
-        Node::new()
-    }
-
-    /// Attempts to pop a value from this queue. Remember that to use this type
-    /// safely you must ensure that there is only one popper at a time.
-    pub fn pop(&self) -> Option<T> {
-        unsafe {
-            // The `tail` node is not actually a used node, but rather a
-            // sentinel from where we should start popping from. Hence, look at
-            // tail's next field and see if we can use it. If we do a pop, then
-            // the current tail node is a candidate for going into the cache.
-            let tail = *self.consumer.tail.get();
-            let next = (*tail).next.load(Ordering::Acquire);
-            if next.is_null() {
-                return None;
-            }
-            assert!((*next).value.is_some());
-            let ret = (*next).value.take();
-
-            *self.consumer.0.tail.get() = next;
-            if self.consumer.cache_bound == 0 {
-                self.consumer.tail_prev.store(tail, Ordering::Release);
-            } else {
-                let cached_nodes = self.consumer.cached_nodes.load(Ordering::Relaxed);
-                if cached_nodes < self.consumer.cache_bound && !(*tail).cached {
-                    self.consumer.cached_nodes.store(cached_nodes, Ordering::Relaxed);
-                    (*tail).cached = true;
-                }
-
-                if (*tail).cached {
-                    self.consumer.tail_prev.store(tail, Ordering::Release);
-                } else {
-                    (*self.consumer.tail_prev.load(Ordering::Relaxed))
-                        .next
-                        .store(next, Ordering::Relaxed);
-                    // We have successfully erased all references to 'tail', so
-                    // now we can safely drop it.
-                    let _: Box<Node<T>> = Box::from_raw(tail);
-                }
-            }
-            ret
-        }
-    }
-
-    /// Attempts to peek at the head of the queue, returning `None` if the queue
-    /// has no data currently
-    ///
-    /// # Warning
-    /// The reference returned is invalid if it is not used before the consumer
-    /// pops the value off the queue. If the producer then pushes another value
-    /// onto the queue, it will overwrite the value pointed to by the reference.
-    pub fn peek(&self) -> Option<&mut T> {
-        // This is essentially the same as above with all the popping bits
-        // stripped out.
-        unsafe {
-            let tail = *self.consumer.tail.get();
-            let next = (*tail).next.load(Ordering::Acquire);
-            if next.is_null() { None } else { (*next).value.as_mut() }
-        }
-    }
-
-    pub fn producer_addition(&self) -> &ProducerAddition {
-        &self.producer.addition
-    }
-
-    pub fn consumer_addition(&self) -> &ConsumerAddition {
-        &self.consumer.addition
-    }
-}
-
-impl<T, ProducerAddition, ConsumerAddition> Drop for Queue<T, ProducerAddition, ConsumerAddition> {
-    fn drop(&mut self) {
-        unsafe {
-            let mut cur = *self.producer.first.get();
-            while !cur.is_null() {
-                let next = (*cur).next.load(Ordering::Relaxed);
-                let _n: Box<Node<T>> = Box::from_raw(cur);
-                cur = next;
-            }
-        }
-    }
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod tests {
-    use super::Queue;
-    use crate::sync::mpsc::channel;
-    use crate::sync::Arc;
-    use crate::thread;
-
-    #[test]
-    fn smoke() {
-        unsafe {
-            let queue = Queue::with_additions(0, (), ());
-            queue.push(1);
-            queue.push(2);
-            assert_eq!(queue.pop(), Some(1));
-            assert_eq!(queue.pop(), Some(2));
-            assert_eq!(queue.pop(), None);
-            queue.push(3);
-            queue.push(4);
-            assert_eq!(queue.pop(), Some(3));
-            assert_eq!(queue.pop(), Some(4));
-            assert_eq!(queue.pop(), None);
-        }
-    }
-
-    #[test]
-    fn peek() {
-        unsafe {
-            let queue = Queue::with_additions(0, (), ());
-            queue.push(vec![1]);
-
-            // Ensure the borrowchecker works
-            match queue.peek() {
-                Some(vec) => {
-                    assert_eq!(&*vec, &[1]);
-                }
-                None => unreachable!(),
-            }
-
-            match queue.pop() {
-                Some(vec) => {
-                    assert_eq!(&*vec, &[1]);
-                }
-                None => unreachable!(),
-            }
-        }
-    }
-
-    #[test]
-    fn drop_full() {
-        unsafe {
-            let q: Queue<Box<_>> = Queue::with_additions(0, (), ());
-            q.push(box 1);
-            q.push(box 2);
-        }
-    }
-
-    #[test]
-    fn smoke_bound() {
-        unsafe {
-            let q = Queue::with_additions(0, (), ());
-            q.push(1);
-            q.push(2);
-            assert_eq!(q.pop(), Some(1));
-            assert_eq!(q.pop(), Some(2));
-            assert_eq!(q.pop(), None);
-            q.push(3);
-            q.push(4);
-            assert_eq!(q.pop(), Some(3));
-            assert_eq!(q.pop(), Some(4));
-            assert_eq!(q.pop(), None);
-        }
-    }
-
-    #[test]
-    fn stress() {
-        unsafe {
-            stress_bound(0);
-            stress_bound(1);
-        }
-
-        unsafe fn stress_bound(bound: usize) {
-            let q = Arc::new(Queue::with_additions(bound, (), ()));
-
-            let (tx, rx) = channel();
-            let q2 = q.clone();
-            let _t = thread::spawn(move || {
-                for _ in 0..100000 {
-                    loop {
-                        match q2.pop() {
-                            Some(1) => break,
-                            Some(_) => panic!(),
-                            None => {}
-                        }
-                    }
-                }
-                tx.send(()).unwrap();
-            });
-            for _ in 0..100000 {
-                q.push(1);
-            }
-            rx.recv().unwrap();
-        }
-    }
-}
diff --git a/src/libstd/sync/mpsc/stream.rs b/src/libstd/sync/mpsc/stream.rs
deleted file mode 100644
index 9f7c1af8951..00000000000
--- a/src/libstd/sync/mpsc/stream.rs
+++ /dev/null
@@ -1,453 +0,0 @@
-/// Stream channels
-///
-/// This is the flavor of channels which are optimized for one sender and one
-/// receiver. The sender will be upgraded to a shared channel if the channel is
-/// cloned.
-///
-/// High level implementation details can be found in the comment of the parent
-/// module.
-pub use self::Failure::*;
-use self::Message::*;
-pub use self::UpgradeResult::*;
-
-use core::cmp;
-
-use crate::cell::UnsafeCell;
-use crate::ptr;
-use crate::thread;
-use crate::time::Instant;
-
-use crate::sync::atomic::{AtomicBool, AtomicIsize, AtomicUsize, Ordering};
-use crate::sync::mpsc::blocking::{self, SignalToken};
-use crate::sync::mpsc::spsc_queue as spsc;
-use crate::sync::mpsc::Receiver;
-
-const DISCONNECTED: isize = isize::MIN;
-#[cfg(test)]
-const MAX_STEALS: isize = 5;
-#[cfg(not(test))]
-const MAX_STEALS: isize = 1 << 20;
-
-pub struct Packet<T> {
-    // internal queue for all messages
-    queue: spsc::Queue<Message<T>, ProducerAddition, ConsumerAddition>,
-}
-
-struct ProducerAddition {
-    cnt: AtomicIsize,     // How many items are on this channel
-    to_wake: AtomicUsize, // SignalToken for the blocked thread to wake up
-
-    port_dropped: AtomicBool, // flag if the channel has been destroyed.
-}
-
-struct ConsumerAddition {
-    steals: UnsafeCell<isize>, // How many times has a port received without blocking?
-}
-
-pub enum Failure<T> {
-    Empty,
-    Disconnected,
-    Upgraded(Receiver<T>),
-}
-
-pub enum UpgradeResult {
-    UpSuccess,
-    UpDisconnected,
-    UpWoke(SignalToken),
-}
-
-// Any message could contain an "upgrade request" to a new shared port, so the
-// internal queue it's a queue of T, but rather Message<T>
-enum Message<T> {
-    Data(T),
-    GoUp(Receiver<T>),
-}
-
-impl<T> Packet<T> {
-    pub fn new() -> Packet<T> {
-        Packet {
-            queue: unsafe {
-                spsc::Queue::with_additions(
-                    128,
-                    ProducerAddition {
-                        cnt: AtomicIsize::new(0),
-                        to_wake: AtomicUsize::new(0),
-
-                        port_dropped: AtomicBool::new(false),
-                    },
-                    ConsumerAddition { steals: UnsafeCell::new(0) },
-                )
-            },
-        }
-    }
-
-    pub fn send(&self, t: T) -> Result<(), T> {
-        // If the other port has deterministically gone away, then definitely
-        // must return the data back up the stack. Otherwise, the data is
-        // considered as being sent.
-        if self.queue.producer_addition().port_dropped.load(Ordering::SeqCst) {
-            return Err(t);
-        }
-
-        match self.do_send(Data(t)) {
-            UpSuccess | UpDisconnected => {}
-            UpWoke(token) => {
-                token.signal();
-            }
-        }
-        Ok(())
-    }
-
-    pub fn upgrade(&self, up: Receiver<T>) -> UpgradeResult {
-        // If the port has gone away, then there's no need to proceed any
-        // further.
-        if self.queue.producer_addition().port_dropped.load(Ordering::SeqCst) {
-            return UpDisconnected;
-        }
-
-        self.do_send(GoUp(up))
-    }
-
-    fn do_send(&self, t: Message<T>) -> UpgradeResult {
-        self.queue.push(t);
-        match self.queue.producer_addition().cnt.fetch_add(1, Ordering::SeqCst) {
-            // As described in the mod's doc comment, -1 == wakeup
-            -1 => UpWoke(self.take_to_wake()),
-            // As as described before, SPSC queues must be >= -2
-            -2 => UpSuccess,
-
-            // Be sure to preserve the disconnected state, and the return value
-            // in this case is going to be whether our data was received or not.
-            // This manifests itself on whether we have an empty queue or not.
-            //
-            // Primarily, are required to drain the queue here because the port
-            // will never remove this data. We can only have at most one item to
-            // drain (the port drains the rest).
-            DISCONNECTED => {
-                self.queue.producer_addition().cnt.store(DISCONNECTED, Ordering::SeqCst);
-                let first = self.queue.pop();
-                let second = self.queue.pop();
-                assert!(second.is_none());
-
-                match first {
-                    Some(..) => UpSuccess,  // we failed to send the data
-                    None => UpDisconnected, // we successfully sent data
-                }
-            }
-
-            // Otherwise we just sent some data on a non-waiting queue, so just
-            // make sure the world is sane and carry on!
-            n => {
-                assert!(n >= 0);
-                UpSuccess
-            }
-        }
-    }
-
-    // Consumes ownership of the 'to_wake' field.
-    fn take_to_wake(&self) -> SignalToken {
-        let ptr = self.queue.producer_addition().to_wake.load(Ordering::SeqCst);
-        self.queue.producer_addition().to_wake.store(0, Ordering::SeqCst);
-        assert!(ptr != 0);
-        unsafe { SignalToken::cast_from_usize(ptr) }
-    }
-
-    // Decrements the count on the channel for a sleeper, returning the sleeper
-    // back if it shouldn't sleep. Note that this is the location where we take
-    // steals into account.
-    fn decrement(&self, token: SignalToken) -> Result<(), SignalToken> {
-        assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), 0);
-        let ptr = unsafe { token.cast_to_usize() };
-        self.queue.producer_addition().to_wake.store(ptr, Ordering::SeqCst);
-
-        let steals = unsafe { ptr::replace(self.queue.consumer_addition().steals.get(), 0) };
-
-        match self.queue.producer_addition().cnt.fetch_sub(1 + steals, Ordering::SeqCst) {
-            DISCONNECTED => {
-                self.queue.producer_addition().cnt.store(DISCONNECTED, Ordering::SeqCst);
-            }
-            // If we factor in our steals and notice that the channel has no
-            // data, we successfully sleep
-            n => {
-                assert!(n >= 0);
-                if n - steals <= 0 {
-                    return Ok(());
-                }
-            }
-        }
-
-        self.queue.producer_addition().to_wake.store(0, Ordering::SeqCst);
-        Err(unsafe { SignalToken::cast_from_usize(ptr) })
-    }
-
-    pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure<T>> {
-        // Optimistic preflight check (scheduling is expensive).
-        match self.try_recv() {
-            Err(Empty) => {}
-            data => return data,
-        }
-
-        // Welp, our channel has no data. Deschedule the current thread and
-        // initiate the blocking protocol.
-        let (wait_token, signal_token) = blocking::tokens();
-        if self.decrement(signal_token).is_ok() {
-            if let Some(deadline) = deadline {
-                let timed_out = !wait_token.wait_max_until(deadline);
-                if timed_out {
-                    self.abort_selection(/* was_upgrade = */ false).map_err(Upgraded)?;
-                }
-            } else {
-                wait_token.wait();
-            }
-        }
-
-        match self.try_recv() {
-            // Messages which actually popped from the queue shouldn't count as
-            // a steal, so offset the decrement here (we already have our
-            // "steal" factored into the channel count above).
-            data @ (Ok(..) | Err(Upgraded(..))) => unsafe {
-                *self.queue.consumer_addition().steals.get() -= 1;
-                data
-            },
-
-            data => data,
-        }
-    }
-
-    pub fn try_recv(&self) -> Result<T, Failure<T>> {
-        match self.queue.pop() {
-            // If we stole some data, record to that effect (this will be
-            // factored into cnt later on).
-            //
-            // Note that we don't allow steals to grow without bound in order to
-            // prevent eventual overflow of either steals or cnt as an overflow
-            // would have catastrophic results. Sometimes, steals > cnt, but
-            // other times cnt > steals, so we don't know the relation between
-            // steals and cnt. This code path is executed only rarely, so we do
-            // a pretty slow operation, of swapping 0 into cnt, taking steals
-            // down as much as possible (without going negative), and then
-            // adding back in whatever we couldn't factor into steals.
-            Some(data) => unsafe {
-                if *self.queue.consumer_addition().steals.get() > MAX_STEALS {
-                    match self.queue.producer_addition().cnt.swap(0, Ordering::SeqCst) {
-                        DISCONNECTED => {
-                            self.queue
-                                .producer_addition()
-                                .cnt
-                                .store(DISCONNECTED, Ordering::SeqCst);
-                        }
-                        n => {
-                            let m = cmp::min(n, *self.queue.consumer_addition().steals.get());
-                            *self.queue.consumer_addition().steals.get() -= m;
-                            self.bump(n - m);
-                        }
-                    }
-                    assert!(*self.queue.consumer_addition().steals.get() >= 0);
-                }
-                *self.queue.consumer_addition().steals.get() += 1;
-                match data {
-                    Data(t) => Ok(t),
-                    GoUp(up) => Err(Upgraded(up)),
-                }
-            },
-
-            None => {
-                match self.queue.producer_addition().cnt.load(Ordering::SeqCst) {
-                    n if n != DISCONNECTED => Err(Empty),
-
-                    // This is a little bit of a tricky case. We failed to pop
-                    // data above, and then we have viewed that the channel is
-                    // disconnected. In this window more data could have been
-                    // sent on the channel. It doesn't really make sense to
-                    // return that the channel is disconnected when there's
-                    // actually data on it, so be extra sure there's no data by
-                    // popping one more time.
-                    //
-                    // We can ignore steals because the other end is
-                    // disconnected and we'll never need to really factor in our
-                    // steals again.
-                    _ => match self.queue.pop() {
-                        Some(Data(t)) => Ok(t),
-                        Some(GoUp(up)) => Err(Upgraded(up)),
-                        None => Err(Disconnected),
-                    },
-                }
-            }
-        }
-    }
-
-    pub fn drop_chan(&self) {
-        // Dropping a channel is pretty simple, we just flag it as disconnected
-        // and then wakeup a blocker if there is one.
-        match self.queue.producer_addition().cnt.swap(DISCONNECTED, Ordering::SeqCst) {
-            -1 => {
-                self.take_to_wake().signal();
-            }
-            DISCONNECTED => {}
-            n => {
-                assert!(n >= 0);
-            }
-        }
-    }
-
-    pub fn drop_port(&self) {
-        // Dropping a port seems like a fairly trivial thing. In theory all we
-        // need to do is flag that we're disconnected and then everything else
-        // can take over (we don't have anyone to wake up).
-        //
-        // The catch for Ports is that we want to drop the entire contents of
-        // the queue. There are multiple reasons for having this property, the
-        // largest of which is that if another chan is waiting in this channel
-        // (but not received yet), then waiting on that port will cause a
-        // deadlock.
-        //
-        // So if we accept that we must now destroy the entire contents of the
-        // queue, this code may make a bit more sense. The tricky part is that
-        // we can't let any in-flight sends go un-dropped, we have to make sure
-        // *everything* is dropped and nothing new will come onto the channel.
-
-        // The first thing we do is set a flag saying that we're done for. All
-        // sends are gated on this flag, so we're immediately guaranteed that
-        // there are a bounded number of active sends that we'll have to deal
-        // with.
-        self.queue.producer_addition().port_dropped.store(true, Ordering::SeqCst);
-
-        // Now that we're guaranteed to deal with a bounded number of senders,
-        // we need to drain the queue. This draining process happens atomically
-        // with respect to the "count" of the channel. If the count is nonzero
-        // (with steals taken into account), then there must be data on the
-        // channel. In this case we drain everything and then try again. We will
-        // continue to fail while active senders send data while we're dropping
-        // data, but eventually we're guaranteed to break out of this loop
-        // (because there is a bounded number of senders).
-        let mut steals = unsafe { *self.queue.consumer_addition().steals.get() };
-        while {
-            let cnt = self.queue.producer_addition().cnt.compare_and_swap(
-                steals,
-                DISCONNECTED,
-                Ordering::SeqCst,
-            );
-            cnt != DISCONNECTED && cnt != steals
-        } {
-            while self.queue.pop().is_some() {
-                steals += 1;
-            }
-        }
-
-        // At this point in time, we have gated all future senders from sending,
-        // and we have flagged the channel as being disconnected. The senders
-        // still have some responsibility, however, because some sends may not
-        // complete until after we flag the disconnection. There are more
-        // details in the sending methods that see DISCONNECTED
-    }
-
-    ////////////////////////////////////////////////////////////////////////////
-    // select implementation
-    ////////////////////////////////////////////////////////////////////////////
-
-    // increment the count on the channel (used for selection)
-    fn bump(&self, amt: isize) -> isize {
-        match self.queue.producer_addition().cnt.fetch_add(amt, Ordering::SeqCst) {
-            DISCONNECTED => {
-                self.queue.producer_addition().cnt.store(DISCONNECTED, Ordering::SeqCst);
-                DISCONNECTED
-            }
-            n => n,
-        }
-    }
-
-    // Removes a previous thread from being blocked in this port
-    pub fn abort_selection(&self, was_upgrade: bool) -> Result<bool, Receiver<T>> {
-        // If we're aborting selection after upgrading from a oneshot, then
-        // we're guarantee that no one is waiting. The only way that we could
-        // have seen the upgrade is if data was actually sent on the channel
-        // half again. For us, this means that there is guaranteed to be data on
-        // this channel. Furthermore, we're guaranteed that there was no
-        // start_selection previously, so there's no need to modify `self.cnt`
-        // at all.
-        //
-        // Hence, because of these invariants, we immediately return `Ok(true)`.
-        // Note that the data may not actually be sent on the channel just yet.
-        // The other end could have flagged the upgrade but not sent data to
-        // this end. This is fine because we know it's a small bounded windows
-        // of time until the data is actually sent.
-        if was_upgrade {
-            assert_eq!(unsafe { *self.queue.consumer_addition().steals.get() }, 0);
-            assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), 0);
-            return Ok(true);
-        }
-
-        // We want to make sure that the count on the channel goes non-negative,
-        // and in the stream case we can have at most one steal, so just assume
-        // that we had one steal.
-        let steals = 1;
-        let prev = self.bump(steals + 1);
-
-        // If we were previously disconnected, then we know for sure that there
-        // is no thread in to_wake, so just keep going
-        let has_data = if prev == DISCONNECTED {
-            assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), 0);
-            true // there is data, that data is that we're disconnected
-        } else {
-            let cur = prev + steals + 1;
-            assert!(cur >= 0);
-
-            // If the previous count was negative, then we just made things go
-            // positive, hence we passed the -1 boundary and we're responsible
-            // for removing the to_wake() field and trashing it.
-            //
-            // If the previous count was positive then we're in a tougher
-            // situation. A possible race is that a sender just incremented
-            // through -1 (meaning it's going to try to wake a thread up), but it
-            // hasn't yet read the to_wake. In order to prevent a future recv()
-            // from waking up too early (this sender picking up the plastered
-            // over to_wake), we spin loop here waiting for to_wake to be 0.
-            // Note that this entire select() implementation needs an overhaul,
-            // and this is *not* the worst part of it, so this is not done as a
-            // final solution but rather out of necessity for now to get
-            // something working.
-            if prev < 0 {
-                drop(self.take_to_wake());
-            } else {
-                while self.queue.producer_addition().to_wake.load(Ordering::SeqCst) != 0 {
-                    thread::yield_now();
-                }
-            }
-            unsafe {
-                assert_eq!(*self.queue.consumer_addition().steals.get(), 0);
-                *self.queue.consumer_addition().steals.get() = steals;
-            }
-
-            // if we were previously positive, then there's surely data to
-            // receive
-            prev >= 0
-        };
-
-        // Now that we've determined that this queue "has data", we peek at the
-        // queue to see if the data is an upgrade or not. If it's an upgrade,
-        // then we need to destroy this port and abort selection on the
-        // upgraded port.
-        if has_data {
-            match self.queue.peek() {
-                Some(&mut GoUp(..)) => match self.queue.pop() {
-                    Some(GoUp(port)) => Err(port),
-                    _ => unreachable!(),
-                },
-                _ => Ok(true),
-            }
-        } else {
-            Ok(false)
-        }
-    }
-}
-
-impl<T> Drop for Packet<T> {
-    fn drop(&mut self) {
-        // Note that this load is not only an assert for correctness about
-        // disconnection, but also a proper fence before the read of
-        // `to_wake`, so this assert cannot be removed with also removing
-        // the `to_wake` assert.
-        assert_eq!(self.queue.producer_addition().cnt.load(Ordering::SeqCst), DISCONNECTED);
-        assert_eq!(self.queue.producer_addition().to_wake.load(Ordering::SeqCst), 0);
-    }
-}
diff --git a/src/libstd/sync/mpsc/sync.rs b/src/libstd/sync/mpsc/sync.rs
deleted file mode 100644
index 733761671a0..00000000000
--- a/src/libstd/sync/mpsc/sync.rs
+++ /dev/null
@@ -1,495 +0,0 @@
-use self::Blocker::*;
-/// Synchronous channels/ports
-///
-/// This channel implementation differs significantly from the asynchronous
-/// implementations found next to it (oneshot/stream/share). This is an
-/// implementation of a synchronous, bounded buffer channel.
-///
-/// Each channel is created with some amount of backing buffer, and sends will
-/// *block* until buffer space becomes available. A buffer size of 0 is valid,
-/// which means that every successful send is paired with a successful recv.
-///
-/// This flavor of channels defines a new `send_opt` method for channels which
-/// is the method by which a message is sent but the thread does not panic if it
-/// cannot be delivered.
-///
-/// Another major difference is that send() will *always* return back the data
-/// if it couldn't be sent. This is because it is deterministically known when
-/// the data is received and when it is not received.
-///
-/// Implementation-wise, it can all be summed up with "use a mutex plus some
-/// logic". The mutex used here is an OS native mutex, meaning that no user code
-/// is run inside of the mutex (to prevent context switching). This
-/// implementation shares almost all code for the buffered and unbuffered cases
-/// of a synchronous channel. There are a few branches for the unbuffered case,
-/// but they're mostly just relevant to blocking senders.
-pub use self::Failure::*;
-
-use core::intrinsics::abort;
-use core::mem;
-use core::ptr;
-
-use crate::sync::atomic::{AtomicUsize, Ordering};
-use crate::sync::mpsc::blocking::{self, SignalToken, WaitToken};
-use crate::sync::{Mutex, MutexGuard};
-use crate::time::Instant;
-
-const MAX_REFCOUNT: usize = (isize::MAX) as usize;
-
-pub struct Packet<T> {
-    /// Only field outside of the mutex. Just done for kicks, but mainly because
-    /// the other shared channel already had the code implemented
-    channels: AtomicUsize,
-
-    lock: Mutex<State<T>>,
-}
-
-unsafe impl<T: Send> Send for Packet<T> {}
-
-unsafe impl<T: Send> Sync for Packet<T> {}
-
-struct State<T> {
-    disconnected: bool, // Is the channel disconnected yet?
-    queue: Queue,       // queue of senders waiting to send data
-    blocker: Blocker,   // currently blocked thread on this channel
-    buf: Buffer<T>,     // storage for buffered messages
-    cap: usize,         // capacity of this channel
-
-    /// A curious flag used to indicate whether a sender failed or succeeded in
-    /// blocking. This is used to transmit information back to the thread that it
-    /// must dequeue its message from the buffer because it was not received.
-    /// This is only relevant in the 0-buffer case. This obviously cannot be
-    /// safely constructed, but it's guaranteed to always have a valid pointer
-    /// value.
-    canceled: Option<&'static mut bool>,
-}
-
-unsafe impl<T: Send> Send for State<T> {}
-
-/// Possible flavors of threads who can be blocked on this channel.
-enum Blocker {
-    BlockedSender(SignalToken),
-    BlockedReceiver(SignalToken),
-    NoneBlocked,
-}
-
-/// Simple queue for threading threads together. Nodes are stack-allocated, so
-/// this structure is not safe at all
-struct Queue {
-    head: *mut Node,
-    tail: *mut Node,
-}
-
-struct Node {
-    token: Option<SignalToken>,
-    next: *mut Node,
-}
-
-unsafe impl Send for Node {}
-
-/// A simple ring-buffer
-struct Buffer<T> {
-    buf: Vec<Option<T>>,
-    start: usize,
-    size: usize,
-}
-
-#[derive(Debug)]
-pub enum Failure {
-    Empty,
-    Disconnected,
-}
-
-/// Atomically blocks the current thread, placing it into `slot`, unlocking `lock`
-/// in the meantime. This re-locks the mutex upon returning.
-fn wait<'a, 'b, T>(
-    lock: &'a Mutex<State<T>>,
-    mut guard: MutexGuard<'b, State<T>>,
-    f: fn(SignalToken) -> Blocker,
-) -> MutexGuard<'a, State<T>> {
-    let (wait_token, signal_token) = blocking::tokens();
-    match mem::replace(&mut guard.blocker, f(signal_token)) {
-        NoneBlocked => {}
-        _ => unreachable!(),
-    }
-    drop(guard); // unlock
-    wait_token.wait(); // block
-    lock.lock().unwrap() // relock
-}
-
-/// Same as wait, but waiting at most until `deadline`.
-fn wait_timeout_receiver<'a, 'b, T>(
-    lock: &'a Mutex<State<T>>,
-    deadline: Instant,
-    mut guard: MutexGuard<'b, State<T>>,
-    success: &mut bool,
-) -> MutexGuard<'a, State<T>> {
-    let (wait_token, signal_token) = blocking::tokens();
-    match mem::replace(&mut guard.blocker, BlockedReceiver(signal_token)) {
-        NoneBlocked => {}
-        _ => unreachable!(),
-    }
-    drop(guard); // unlock
-    *success = wait_token.wait_max_until(deadline); // block
-    let mut new_guard = lock.lock().unwrap(); // relock
-    if !*success {
-        abort_selection(&mut new_guard);
-    }
-    new_guard
-}
-
-fn abort_selection<T>(guard: &mut MutexGuard<'_, State<T>>) -> bool {
-    match mem::replace(&mut guard.blocker, NoneBlocked) {
-        NoneBlocked => true,
-        BlockedSender(token) => {
-            guard.blocker = BlockedSender(token);
-            true
-        }
-        BlockedReceiver(token) => {
-            drop(token);
-            false
-        }
-    }
-}
-
-/// Wakes up a thread, dropping the lock at the correct time
-fn wakeup<T>(token: SignalToken, guard: MutexGuard<'_, State<T>>) {
-    // We need to be careful to wake up the waiting thread *outside* of the mutex
-    // in case it incurs a context switch.
-    drop(guard);
-    token.signal();
-}
-
-impl<T> Packet<T> {
-    pub fn new(capacity: usize) -> Packet<T> {
-        Packet {
-            channels: AtomicUsize::new(1),
-            lock: Mutex::new(State {
-                disconnected: false,
-                blocker: NoneBlocked,
-                cap: capacity,
-                canceled: None,
-                queue: Queue { head: ptr::null_mut(), tail: ptr::null_mut() },
-                buf: Buffer {
-                    buf: (0..capacity + if capacity == 0 { 1 } else { 0 }).map(|_| None).collect(),
-                    start: 0,
-                    size: 0,
-                },
-            }),
-        }
-    }
-
-    // wait until a send slot is available, returning locked access to
-    // the channel state.
-    fn acquire_send_slot(&self) -> MutexGuard<'_, State<T>> {
-        let mut node = Node { token: None, next: ptr::null_mut() };
-        loop {
-            let mut guard = self.lock.lock().unwrap();
-            // are we ready to go?
-            if guard.disconnected || guard.buf.size() < guard.buf.capacity() {
-                return guard;
-            }
-            // no room; actually block
-            let wait_token = guard.queue.enqueue(&mut node);
-            drop(guard);
-            wait_token.wait();
-        }
-    }
-
-    pub fn send(&self, t: T) -> Result<(), T> {
-        let mut guard = self.acquire_send_slot();
-        if guard.disconnected {
-            return Err(t);
-        }
-        guard.buf.enqueue(t);
-
-        match mem::replace(&mut guard.blocker, NoneBlocked) {
-            // if our capacity is 0, then we need to wait for a receiver to be
-            // available to take our data. After waiting, we check again to make
-            // sure the port didn't go away in the meantime. If it did, we need
-            // to hand back our data.
-            NoneBlocked if guard.cap == 0 => {
-                let mut canceled = false;
-                assert!(guard.canceled.is_none());
-                guard.canceled = Some(unsafe { mem::transmute(&mut canceled) });
-                let mut guard = wait(&self.lock, guard, BlockedSender);
-                if canceled { Err(guard.buf.dequeue()) } else { Ok(()) }
-            }
-
-            // success, we buffered some data
-            NoneBlocked => Ok(()),
-
-            // success, someone's about to receive our buffered data.
-            BlockedReceiver(token) => {
-                wakeup(token, guard);
-                Ok(())
-            }
-
-            BlockedSender(..) => panic!("lolwut"),
-        }
-    }
-
-    pub fn try_send(&self, t: T) -> Result<(), super::TrySendError<T>> {
-        let mut guard = self.lock.lock().unwrap();
-        if guard.disconnected {
-            Err(super::TrySendError::Disconnected(t))
-        } else if guard.buf.size() == guard.buf.capacity() {
-            Err(super::TrySendError::Full(t))
-        } else if guard.cap == 0 {
-            // With capacity 0, even though we have buffer space we can't
-            // transfer the data unless there's a receiver waiting.
-            match mem::replace(&mut guard.blocker, NoneBlocked) {
-                NoneBlocked => Err(super::TrySendError::Full(t)),
-                BlockedSender(..) => unreachable!(),
-                BlockedReceiver(token) => {
-                    guard.buf.enqueue(t);
-                    wakeup(token, guard);
-                    Ok(())
-                }
-            }
-        } else {
-            // If the buffer has some space and the capacity isn't 0, then we
-            // just enqueue the data for later retrieval, ensuring to wake up
-            // any blocked receiver if there is one.
-            assert!(guard.buf.size() < guard.buf.capacity());
-            guard.buf.enqueue(t);
-            match mem::replace(&mut guard.blocker, NoneBlocked) {
-                BlockedReceiver(token) => wakeup(token, guard),
-                NoneBlocked => {}
-                BlockedSender(..) => unreachable!(),
-            }
-            Ok(())
-        }
-    }
-
-    // Receives a message from this channel
-    //
-    // When reading this, remember that there can only ever be one receiver at
-    // time.
-    pub fn recv(&self, deadline: Option<Instant>) -> Result<T, Failure> {
-        let mut guard = self.lock.lock().unwrap();
-
-        let mut woke_up_after_waiting = false;
-        // Wait for the buffer to have something in it. No need for a
-        // while loop because we're the only receiver.
-        if !guard.disconnected && guard.buf.size() == 0 {
-            if let Some(deadline) = deadline {
-                guard =
-                    wait_timeout_receiver(&self.lock, deadline, guard, &mut woke_up_after_waiting);
-            } else {
-                guard = wait(&self.lock, guard, BlockedReceiver);
-                woke_up_after_waiting = true;
-            }
-        }
-
-        // N.B., channel could be disconnected while waiting, so the order of
-        // these conditionals is important.
-        if guard.disconnected && guard.buf.size() == 0 {
-            return Err(Disconnected);
-        }
-
-        // Pick up the data, wake up our neighbors, and carry on
-        assert!(guard.buf.size() > 0 || (deadline.is_some() && !woke_up_after_waiting));
-
-        if guard.buf.size() == 0 {
-            return Err(Empty);
-        }
-
-        let ret = guard.buf.dequeue();
-        self.wakeup_senders(woke_up_after_waiting, guard);
-        Ok(ret)
-    }
-
-    pub fn try_recv(&self) -> Result<T, Failure> {
-        let mut guard = self.lock.lock().unwrap();
-
-        // Easy cases first
-        if guard.disconnected && guard.buf.size() == 0 {
-            return Err(Disconnected);
-        }
-        if guard.buf.size() == 0 {
-            return Err(Empty);
-        }
-
-        // Be sure to wake up neighbors
-        let ret = Ok(guard.buf.dequeue());
-        self.wakeup_senders(false, guard);
-        ret
-    }
-
-    // Wake up pending senders after some data has been received
-    //
-    // * `waited` - flag if the receiver blocked to receive some data, or if it
-    //              just picked up some data on the way out
-    // * `guard` - the lock guard that is held over this channel's lock
-    fn wakeup_senders(&self, waited: bool, mut guard: MutexGuard<'_, State<T>>) {
-        let pending_sender1: Option<SignalToken> = guard.queue.dequeue();
-
-        // If this is a no-buffer channel (cap == 0), then if we didn't wait we
-        // need to ACK the sender. If we waited, then the sender waking us up
-        // was already the ACK.
-        let pending_sender2 = if guard.cap == 0 && !waited {
-            match mem::replace(&mut guard.blocker, NoneBlocked) {
-                NoneBlocked => None,
-                BlockedReceiver(..) => unreachable!(),
-                BlockedSender(token) => {
-                    guard.canceled.take();
-                    Some(token)
-                }
-            }
-        } else {
-            None
-        };
-        mem::drop(guard);
-
-        // only outside of the lock do we wake up the pending threads
-        if let Some(token) = pending_sender1 {
-            token.signal();
-        }
-        if let Some(token) = pending_sender2 {
-            token.signal();
-        }
-    }
-
-    // Prepares this shared packet for a channel clone, essentially just bumping
-    // a refcount.
-    pub fn clone_chan(&self) {
-        let old_count = self.channels.fetch_add(1, Ordering::SeqCst);
-
-        // See comments on Arc::clone() on why we do this (for `mem::forget`).
-        if old_count > MAX_REFCOUNT {
-            abort();
-        }
-    }
-
-    pub fn drop_chan(&self) {
-        // Only flag the channel as disconnected if we're the last channel
-        match self.channels.fetch_sub(1, Ordering::SeqCst) {
-            1 => {}
-            _ => return,
-        }
-
-        // Not much to do other than wake up a receiver if one's there
-        let mut guard = self.lock.lock().unwrap();
-        if guard.disconnected {
-            return;
-        }
-        guard.disconnected = true;
-        match mem::replace(&mut guard.blocker, NoneBlocked) {
-            NoneBlocked => {}
-            BlockedSender(..) => unreachable!(),
-            BlockedReceiver(token) => wakeup(token, guard),
-        }
-    }
-
-    pub fn drop_port(&self) {
-        let mut guard = self.lock.lock().unwrap();
-
-        if guard.disconnected {
-            return;
-        }
-        guard.disconnected = true;
-
-        // If the capacity is 0, then the sender may want its data back after
-        // we're disconnected. Otherwise it's now our responsibility to destroy
-        // the buffered data. As with many other portions of this code, this
-        // needs to be careful to destroy the data *outside* of the lock to
-        // prevent deadlock.
-        let _data = if guard.cap != 0 { mem::take(&mut guard.buf.buf) } else { Vec::new() };
-        let mut queue =
-            mem::replace(&mut guard.queue, Queue { head: ptr::null_mut(), tail: ptr::null_mut() });
-
-        let waiter = match mem::replace(&mut guard.blocker, NoneBlocked) {
-            NoneBlocked => None,
-            BlockedSender(token) => {
-                *guard.canceled.take().unwrap() = true;
-                Some(token)
-            }
-            BlockedReceiver(..) => unreachable!(),
-        };
-        mem::drop(guard);
-
-        while let Some(token) = queue.dequeue() {
-            token.signal();
-        }
-        if let Some(token) = waiter {
-            token.signal();
-        }
-    }
-}
-
-impl<T> Drop for Packet<T> {
-    fn drop(&mut self) {
-        assert_eq!(self.channels.load(Ordering::SeqCst), 0);
-        let mut guard = self.lock.lock().unwrap();
-        assert!(guard.queue.dequeue().is_none());
-        assert!(guard.canceled.is_none());
-    }
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// Buffer, a simple ring buffer backed by Vec<T>
-////////////////////////////////////////////////////////////////////////////////
-
-impl<T> Buffer<T> {
-    fn enqueue(&mut self, t: T) {
-        let pos = (self.start + self.size) % self.buf.len();
-        self.size += 1;
-        let prev = mem::replace(&mut self.buf[pos], Some(t));
-        assert!(prev.is_none());
-    }
-
-    fn dequeue(&mut self) -> T {
-        let start = self.start;
-        self.size -= 1;
-        self.start = (self.start + 1) % self.buf.len();
-        let result = &mut self.buf[start];
-        result.take().unwrap()
-    }
-
-    fn size(&self) -> usize {
-        self.size
-    }
-    fn capacity(&self) -> usize {
-        self.buf.len()
-    }
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// Queue, a simple queue to enqueue threads with (stack-allocated nodes)
-////////////////////////////////////////////////////////////////////////////////
-
-impl Queue {
-    fn enqueue(&mut self, node: &mut Node) -> WaitToken {
-        let (wait_token, signal_token) = blocking::tokens();
-        node.token = Some(signal_token);
-        node.next = ptr::null_mut();
-
-        if self.tail.is_null() {
-            self.head = node as *mut Node;
-            self.tail = node as *mut Node;
-        } else {
-            unsafe {
-                (*self.tail).next = node as *mut Node;
-                self.tail = node as *mut Node;
-            }
-        }
-
-        wait_token
-    }
-
-    fn dequeue(&mut self) -> Option<SignalToken> {
-        if self.head.is_null() {
-            return None;
-        }
-        let node = self.head;
-        self.head = unsafe { (*node).next };
-        if self.head.is_null() {
-            self.tail = ptr::null_mut();
-        }
-        unsafe {
-            (*node).next = ptr::null_mut();
-            Some((*node).token.take().unwrap())
-        }
-    }
-}
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
deleted file mode 100644
index 8478457eabf..00000000000
--- a/src/libstd/sync/mutex.rs
+++ /dev/null
@@ -1,767 +0,0 @@
-use crate::cell::UnsafeCell;
-use crate::fmt;
-use crate::mem;
-use crate::ops::{Deref, DerefMut};
-use crate::ptr;
-use crate::sys_common::mutex as sys;
-use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
-
-/// A mutual exclusion primitive useful for protecting shared data
-///
-/// This mutex will block threads waiting for the lock to become available. The
-/// mutex can also be statically initialized or created via a [`new`]
-/// constructor. Each mutex has a type parameter which represents the data that
-/// it is protecting. The data can only be accessed through the RAII guards
-/// returned from [`lock`] and [`try_lock`], which guarantees that the data is only
-/// ever accessed when the mutex is locked.
-///
-/// # Poisoning
-///
-/// The mutexes in this module implement a strategy called "poisoning" where a
-/// mutex is considered poisoned whenever a thread panics while holding the
-/// mutex. Once a mutex is poisoned, all other threads are unable to access the
-/// data by default as it is likely tainted (some invariant is not being
-/// upheld).
-///
-/// For a mutex, this means that the [`lock`] and [`try_lock`] methods return a
-/// [`Result`] which indicates whether a mutex has been poisoned or not. Most
-/// usage of a mutex will simply [`unwrap()`] these results, propagating panics
-/// among threads to ensure that a possibly invalid invariant is not witnessed.
-///
-/// A poisoned mutex, however, does not prevent all access to the underlying
-/// data. The [`PoisonError`] type has an [`into_inner`] method which will return
-/// the guard that would have otherwise been returned on a successful lock. This
-/// allows access to the data, despite the lock being poisoned.
-///
-/// [`new`]: #method.new
-/// [`lock`]: #method.lock
-/// [`try_lock`]: #method.try_lock
-/// [`Result`]: ../../std/result/enum.Result.html
-/// [`unwrap()`]: ../../std/result/enum.Result.html#method.unwrap
-/// [`PoisonError`]: ../../std/sync/struct.PoisonError.html
-/// [`into_inner`]: ../../std/sync/struct.PoisonError.html#method.into_inner
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::{Arc, Mutex};
-/// use std::thread;
-/// use std::sync::mpsc::channel;
-///
-/// const N: usize = 10;
-///
-/// // Spawn a few threads to increment a shared variable (non-atomically), and
-/// // let the main thread know once all increments are done.
-/// //
-/// // Here we're using an Arc to share memory among threads, and the data inside
-/// // the Arc is protected with a mutex.
-/// let data = Arc::new(Mutex::new(0));
-///
-/// let (tx, rx) = channel();
-/// for _ in 0..N {
-///     let (data, tx) = (Arc::clone(&data), tx.clone());
-///     thread::spawn(move || {
-///         // The shared state can only be accessed once the lock is held.
-///         // Our non-atomic increment is safe because we're the only thread
-///         // which can access the shared state when the lock is held.
-///         //
-///         // We unwrap() the return value to assert that we are not expecting
-///         // threads to ever fail while holding the lock.
-///         let mut data = data.lock().unwrap();
-///         *data += 1;
-///         if *data == N {
-///             tx.send(()).unwrap();
-///         }
-///         // the lock is unlocked here when `data` goes out of scope.
-///     });
-/// }
-///
-/// rx.recv().unwrap();
-/// ```
-///
-/// To recover from a poisoned mutex:
-///
-/// ```
-/// use std::sync::{Arc, Mutex};
-/// use std::thread;
-///
-/// let lock = Arc::new(Mutex::new(0_u32));
-/// let lock2 = lock.clone();
-///
-/// let _ = thread::spawn(move || -> () {
-///     // This thread will acquire the mutex first, unwrapping the result of
-///     // `lock` because the lock has not been poisoned.
-///     let _guard = lock2.lock().unwrap();
-///
-///     // This panic while holding the lock (`_guard` is in scope) will poison
-///     // the mutex.
-///     panic!();
-/// }).join();
-///
-/// // The lock is poisoned by this point, but the returned result can be
-/// // pattern matched on to return the underlying guard on both branches.
-/// let mut guard = match lock.lock() {
-///     Ok(guard) => guard,
-///     Err(poisoned) => poisoned.into_inner(),
-/// };
-///
-/// *guard += 1;
-/// ```
-///
-/// It is sometimes necessary to manually drop the mutex guard to unlock it
-/// sooner than the end of the enclosing scope.
-///
-/// ```
-/// use std::sync::{Arc, Mutex};
-/// use std::thread;
-///
-/// const N: usize = 3;
-///
-/// let data_mutex = Arc::new(Mutex::new(vec![1, 2, 3, 4]));
-/// let res_mutex = Arc::new(Mutex::new(0));
-///
-/// let mut threads = Vec::with_capacity(N);
-/// (0..N).for_each(|_| {
-///     let data_mutex_clone = Arc::clone(&data_mutex);
-///     let res_mutex_clone = Arc::clone(&res_mutex);
-///
-///     threads.push(thread::spawn(move || {
-///         let mut data = data_mutex_clone.lock().unwrap();
-///         // This is the result of some important and long-ish work.
-///         let result = data.iter().fold(0, |acc, x| acc + x * 2);
-///         data.push(result);
-///         drop(data);
-///         *res_mutex_clone.lock().unwrap() += result;
-///     }));
-/// });
-///
-/// let mut data = data_mutex.lock().unwrap();
-/// // This is the result of some important and long-ish work.
-/// let result = data.iter().fold(0, |acc, x| acc + x * 2);
-/// data.push(result);
-/// // We drop the `data` explicitly because it's not necessary anymore and the
-/// // thread still has work to do. This allow other threads to start working on
-/// // the data immediately, without waiting for the rest of the unrelated work
-/// // to be done here.
-/// //
-/// // It's even more important here than in the threads because we `.join` the
-/// // threads after that. If we had not dropped the mutex guard, a thread could
-/// // be waiting forever for it, causing a deadlock.
-/// drop(data);
-/// // Here the mutex guard is not assigned to a variable and so, even if the
-/// // scope does not end after this line, the mutex is still released: there is
-/// // no deadlock.
-/// *res_mutex.lock().unwrap() += result;
-///
-/// threads.into_iter().for_each(|thread| {
-///     thread
-///         .join()
-///         .expect("The thread creating or execution failed !")
-/// });
-///
-/// assert_eq!(*res_mutex.lock().unwrap(), 800);
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(test), rustc_diagnostic_item = "mutex_type")]
-pub struct Mutex<T: ?Sized> {
-    // Note that this mutex is in a *box*, not inlined into the struct itself.
-    // Once a native mutex has been used once, its address can never change (it
-    // can't be moved). This mutex type can be safely moved at any time, so to
-    // ensure that the native mutex is used correctly we box the inner mutex to
-    // give it a constant address.
-    inner: Box<sys::Mutex>,
-    poison: poison::Flag,
-    data: UnsafeCell<T>,
-}
-
-// these are the only places where `T: Send` matters; all other
-// functionality works fine on a single thread.
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
-
-/// An RAII implementation of a "scoped lock" of a mutex. When this structure is
-/// dropped (falls out of scope), the lock will be unlocked.
-///
-/// The data protected by the mutex can be accessed through this guard via its
-/// [`Deref`] and [`DerefMut`] implementations.
-///
-/// This structure is created by the [`lock`] and [`try_lock`] methods on
-/// [`Mutex`].
-///
-/// [`Deref`]: ../../std/ops/trait.Deref.html
-/// [`DerefMut`]: ../../std/ops/trait.DerefMut.html
-/// [`lock`]: struct.Mutex.html#method.lock
-/// [`try_lock`]: struct.Mutex.html#method.try_lock
-/// [`Mutex`]: struct.Mutex.html
-#[must_use = "if unused the Mutex will immediately unlock"]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct MutexGuard<'a, T: ?Sized + 'a> {
-    lock: &'a Mutex<T>,
-    poison: poison::Guard,
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> !Send for MutexGuard<'_, T> {}
-#[stable(feature = "mutexguard", since = "1.19.0")]
-unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
-
-impl<T> Mutex<T> {
-    /// Creates a new mutex in an unlocked state ready for use.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Mutex;
-    ///
-    /// let mutex = Mutex::new(0);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new(t: T) -> Mutex<T> {
-        let mut m = Mutex {
-            inner: box sys::Mutex::new(),
-            poison: poison::Flag::new(),
-            data: UnsafeCell::new(t),
-        };
-        unsafe {
-            m.inner.init();
-        }
-        m
-    }
-}
-
-impl<T: ?Sized> Mutex<T> {
-    /// Acquires a mutex, blocking the current thread until it is able to do so.
-    ///
-    /// This function will block the local thread until it is available to acquire
-    /// the mutex. Upon returning, the thread is the only thread with the lock
-    /// held. An RAII guard is returned to allow scoped unlock of the lock. When
-    /// the guard goes out of scope, the mutex will be unlocked.
-    ///
-    /// The exact behavior on locking a mutex in the thread which already holds
-    /// the lock is left unspecified. However, this function will not return on
-    /// the second call (it might panic or deadlock, for example).
-    ///
-    /// # Errors
-    ///
-    /// If another user of this mutex panicked while holding the mutex, then
-    /// this call will return an error once the mutex is acquired.
-    ///
-    /// # Panics
-    ///
-    /// This function might panic when called if the lock is already held by
-    /// the current thread.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex};
-    /// use std::thread;
-    ///
-    /// let mutex = Arc::new(Mutex::new(0));
-    /// let c_mutex = mutex.clone();
-    ///
-    /// thread::spawn(move || {
-    ///     *c_mutex.lock().unwrap() = 10;
-    /// }).join().expect("thread::spawn failed");
-    /// assert_eq!(*mutex.lock().unwrap(), 10);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn lock(&self) -> LockResult<MutexGuard<'_, T>> {
-        unsafe {
-            self.inner.raw_lock();
-            MutexGuard::new(self)
-        }
-    }
-
-    /// Attempts to acquire this lock.
-    ///
-    /// If the lock could not be acquired at this time, then [`Err`] is returned.
-    /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
-    /// guard is dropped.
-    ///
-    /// This function does not block.
-    ///
-    /// # Errors
-    ///
-    /// If another user of this mutex panicked while holding the mutex, then
-    /// this call will return failure if the mutex would otherwise be
-    /// acquired.
-    ///
-    /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex};
-    /// use std::thread;
-    ///
-    /// let mutex = Arc::new(Mutex::new(0));
-    /// let c_mutex = mutex.clone();
-    ///
-    /// thread::spawn(move || {
-    ///     let mut lock = c_mutex.try_lock();
-    ///     if let Ok(ref mut mutex) = lock {
-    ///         **mutex = 10;
-    ///     } else {
-    ///         println!("try_lock failed");
-    ///     }
-    /// }).join().expect("thread::spawn failed");
-    /// assert_eq!(*mutex.lock().unwrap(), 10);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn try_lock(&self) -> TryLockResult<MutexGuard<'_, T>> {
-        unsafe {
-            if self.inner.try_lock() {
-                Ok(MutexGuard::new(self)?)
-            } else {
-                Err(TryLockError::WouldBlock)
-            }
-        }
-    }
-
-    /// Determines whether the mutex is poisoned.
-    ///
-    /// If another thread is active, the mutex can still become poisoned at any
-    /// time. You should not trust a `false` value for program correctness
-    /// without additional synchronization.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, Mutex};
-    /// use std::thread;
-    ///
-    /// let mutex = Arc::new(Mutex::new(0));
-    /// let c_mutex = mutex.clone();
-    ///
-    /// let _ = thread::spawn(move || {
-    ///     let _lock = c_mutex.lock().unwrap();
-    ///     panic!(); // the mutex gets poisoned
-    /// }).join();
-    /// assert_eq!(mutex.is_poisoned(), true);
-    /// ```
-    #[inline]
-    #[stable(feature = "sync_poison", since = "1.2.0")]
-    pub fn is_poisoned(&self) -> bool {
-        self.poison.get()
-    }
-
-    /// Consumes this mutex, returning the underlying data.
-    ///
-    /// # Errors
-    ///
-    /// If another user of this mutex panicked while holding the mutex, then
-    /// this call will return an error instead.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Mutex;
-    ///
-    /// let mutex = Mutex::new(0);
-    /// assert_eq!(mutex.into_inner().unwrap(), 0);
-    /// ```
-    #[stable(feature = "mutex_into_inner", since = "1.6.0")]
-    pub fn into_inner(self) -> LockResult<T>
-    where
-        T: Sized,
-    {
-        // We know statically that there are no outstanding references to
-        // `self` so there's no need to lock the inner mutex.
-        //
-        // To get the inner value, we'd like to call `data.into_inner()`,
-        // but because `Mutex` impl-s `Drop`, we can't move out of it, so
-        // we'll have to destructure it manually instead.
-        unsafe {
-            // Like `let Mutex { inner, poison, data } = self`.
-            let (inner, poison, data) = {
-                let Mutex { ref inner, ref poison, ref data } = self;
-                (ptr::read(inner), ptr::read(poison), ptr::read(data))
-            };
-            mem::forget(self);
-            inner.destroy(); // Keep in sync with the `Drop` impl.
-            drop(inner);
-
-            poison::map_result(poison.borrow(), |_| data.into_inner())
-        }
-    }
-
-    /// Returns a mutable reference to the underlying data.
-    ///
-    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
-    /// take place -- the mutable borrow statically guarantees no locks exist.
-    ///
-    /// # Errors
-    ///
-    /// If another user of this mutex panicked while holding the mutex, then
-    /// this call will return an error instead.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Mutex;
-    ///
-    /// let mut mutex = Mutex::new(0);
-    /// *mutex.get_mut().unwrap() = 10;
-    /// assert_eq!(*mutex.lock().unwrap(), 10);
-    /// ```
-    #[stable(feature = "mutex_get_mut", since = "1.6.0")]
-    pub fn get_mut(&mut self) -> LockResult<&mut T> {
-        // We know statically that there are no other references to `self`, so
-        // there's no need to lock the inner mutex.
-        let data = unsafe { &mut *self.data.get() };
-        poison::map_result(self.poison.borrow(), |_| data)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<#[may_dangle] T: ?Sized> Drop for Mutex<T> {
-    fn drop(&mut self) {
-        // This is actually safe b/c we know that there is no further usage of
-        // this mutex (it's up to the user to arrange for a mutex to get
-        // dropped, that's not our job)
-        //
-        // IMPORTANT: This code must be kept in sync with `Mutex::into_inner`.
-        unsafe { self.inner.destroy() }
-    }
-}
-
-#[stable(feature = "mutex_from", since = "1.24.0")]
-impl<T> From<T> for Mutex<T> {
-    /// Creates a new mutex in an unlocked state ready for use.
-    /// This is equivalent to [`Mutex::new`].
-    ///
-    /// [`Mutex::new`]: ../../std/sync/struct.Mutex.html#method.new
-    fn from(t: T) -> Self {
-        Mutex::new(t)
-    }
-}
-
-#[stable(feature = "mutex_default", since = "1.10.0")]
-impl<T: ?Sized + Default> Default for Mutex<T> {
-    /// Creates a `Mutex<T>`, with the `Default` value for T.
-    fn default() -> Mutex<T> {
-        Mutex::new(Default::default())
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.try_lock() {
-            Ok(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
-            Err(TryLockError::Poisoned(err)) => {
-                f.debug_struct("Mutex").field("data", &&**err.get_ref()).finish()
-            }
-            Err(TryLockError::WouldBlock) => {
-                struct LockedPlaceholder;
-                impl fmt::Debug for LockedPlaceholder {
-                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                        f.write_str("<locked>")
-                    }
-                }
-
-                f.debug_struct("Mutex").field("data", &LockedPlaceholder).finish()
-            }
-        }
-    }
-}
-
-impl<'mutex, T: ?Sized> MutexGuard<'mutex, T> {
-    unsafe fn new(lock: &'mutex Mutex<T>) -> LockResult<MutexGuard<'mutex, T>> {
-        poison::map_result(lock.poison.borrow(), |guard| MutexGuard { lock, poison: guard })
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Deref for MutexGuard<'_, T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        unsafe { &*self.lock.data.get() }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
-    fn deref_mut(&mut self) -> &mut T {
-        unsafe { &mut *self.lock.data.get() }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Drop for MutexGuard<'_, T> {
-    #[inline]
-    fn drop(&mut self) {
-        unsafe {
-            self.lock.poison.done(&self.poison);
-            self.lock.inner.raw_unlock();
-        }
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(&**self, f)
-    }
-}
-
-#[stable(feature = "std_guard_impls", since = "1.20.0")]
-impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        (**self).fmt(f)
-    }
-}
-
-pub fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
-    &guard.lock.inner
-}
-
-pub fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Flag {
-    &guard.lock.poison
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod tests {
-    use crate::sync::atomic::{AtomicUsize, Ordering};
-    use crate::sync::mpsc::channel;
-    use crate::sync::{Arc, Condvar, Mutex};
-    use crate::thread;
-
-    struct Packet<T>(Arc<(Mutex<T>, Condvar)>);
-
-    #[derive(Eq, PartialEq, Debug)]
-    struct NonCopy(i32);
-
-    #[test]
-    fn smoke() {
-        let m = Mutex::new(());
-        drop(m.lock().unwrap());
-        drop(m.lock().unwrap());
-    }
-
-    #[test]
-    fn lots_and_lots() {
-        const J: u32 = 1000;
-        const K: u32 = 3;
-
-        let m = Arc::new(Mutex::new(0));
-
-        fn inc(m: &Mutex<u32>) {
-            for _ in 0..J {
-                *m.lock().unwrap() += 1;
-            }
-        }
-
-        let (tx, rx) = channel();
-        for _ in 0..K {
-            let tx2 = tx.clone();
-            let m2 = m.clone();
-            thread::spawn(move || {
-                inc(&m2);
-                tx2.send(()).unwrap();
-            });
-            let tx2 = tx.clone();
-            let m2 = m.clone();
-            thread::spawn(move || {
-                inc(&m2);
-                tx2.send(()).unwrap();
-            });
-        }
-
-        drop(tx);
-        for _ in 0..2 * K {
-            rx.recv().unwrap();
-        }
-        assert_eq!(*m.lock().unwrap(), J * K * 2);
-    }
-
-    #[test]
-    fn try_lock() {
-        let m = Mutex::new(());
-        *m.try_lock().unwrap() = ();
-    }
-
-    #[test]
-    fn test_into_inner() {
-        let m = Mutex::new(NonCopy(10));
-        assert_eq!(m.into_inner().unwrap(), NonCopy(10));
-    }
-
-    #[test]
-    fn test_into_inner_drop() {
-        struct Foo(Arc<AtomicUsize>);
-        impl Drop for Foo {
-            fn drop(&mut self) {
-                self.0.fetch_add(1, Ordering::SeqCst);
-            }
-        }
-        let num_drops = Arc::new(AtomicUsize::new(0));
-        let m = Mutex::new(Foo(num_drops.clone()));
-        assert_eq!(num_drops.load(Ordering::SeqCst), 0);
-        {
-            let _inner = m.into_inner().unwrap();
-            assert_eq!(num_drops.load(Ordering::SeqCst), 0);
-        }
-        assert_eq!(num_drops.load(Ordering::SeqCst), 1);
-    }
-
-    #[test]
-    fn test_into_inner_poison() {
-        let m = Arc::new(Mutex::new(NonCopy(10)));
-        let m2 = m.clone();
-        let _ = thread::spawn(move || {
-            let _lock = m2.lock().unwrap();
-            panic!("test panic in inner thread to poison mutex");
-        })
-        .join();
-
-        assert!(m.is_poisoned());
-        match Arc::try_unwrap(m).unwrap().into_inner() {
-            Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
-            Ok(x) => panic!("into_inner of poisoned Mutex is Ok: {:?}", x),
-        }
-    }
-
-    #[test]
-    fn test_get_mut() {
-        let mut m = Mutex::new(NonCopy(10));
-        *m.get_mut().unwrap() = NonCopy(20);
-        assert_eq!(m.into_inner().unwrap(), NonCopy(20));
-    }
-
-    #[test]
-    fn test_get_mut_poison() {
-        let m = Arc::new(Mutex::new(NonCopy(10)));
-        let m2 = m.clone();
-        let _ = thread::spawn(move || {
-            let _lock = m2.lock().unwrap();
-            panic!("test panic in inner thread to poison mutex");
-        })
-        .join();
-
-        assert!(m.is_poisoned());
-        match Arc::try_unwrap(m).unwrap().get_mut() {
-            Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
-            Ok(x) => panic!("get_mut of poisoned Mutex is Ok: {:?}", x),
-        }
-    }
-
-    #[test]
-    fn test_mutex_arc_condvar() {
-        let packet = Packet(Arc::new((Mutex::new(false), Condvar::new())));
-        let packet2 = Packet(packet.0.clone());
-        let (tx, rx) = channel();
-        let _t = thread::spawn(move || {
-            // wait until parent gets in
-            rx.recv().unwrap();
-            let &(ref lock, ref cvar) = &*packet2.0;
-            let mut lock = lock.lock().unwrap();
-            *lock = true;
-            cvar.notify_one();
-        });
-
-        let &(ref lock, ref cvar) = &*packet.0;
-        let mut lock = lock.lock().unwrap();
-        tx.send(()).unwrap();
-        assert!(!*lock);
-        while !*lock {
-            lock = cvar.wait(lock).unwrap();
-        }
-    }
-
-    #[test]
-    fn test_arc_condvar_poison() {
-        let packet = Packet(Arc::new((Mutex::new(1), Condvar::new())));
-        let packet2 = Packet(packet.0.clone());
-        let (tx, rx) = channel();
-
-        let _t = thread::spawn(move || -> () {
-            rx.recv().unwrap();
-            let &(ref lock, ref cvar) = &*packet2.0;
-            let _g = lock.lock().unwrap();
-            cvar.notify_one();
-            // Parent should fail when it wakes up.
-            panic!();
-        });
-
-        let &(ref lock, ref cvar) = &*packet.0;
-        let mut lock = lock.lock().unwrap();
-        tx.send(()).unwrap();
-        while *lock == 1 {
-            match cvar.wait(lock) {
-                Ok(l) => {
-                    lock = l;
-                    assert_eq!(*lock, 1);
-                }
-                Err(..) => break,
-            }
-        }
-    }
-
-    #[test]
-    fn test_mutex_arc_poison() {
-        let arc = Arc::new(Mutex::new(1));
-        assert!(!arc.is_poisoned());
-        let arc2 = arc.clone();
-        let _ = thread::spawn(move || {
-            let lock = arc2.lock().unwrap();
-            assert_eq!(*lock, 2);
-        })
-        .join();
-        assert!(arc.lock().is_err());
-        assert!(arc.is_poisoned());
-    }
-
-    #[test]
-    fn test_mutex_arc_nested() {
-        // Tests nested mutexes and access
-        // to underlying data.
-        let arc = Arc::new(Mutex::new(1));
-        let arc2 = Arc::new(Mutex::new(arc));
-        let (tx, rx) = channel();
-        let _t = thread::spawn(move || {
-            let lock = arc2.lock().unwrap();
-            let lock2 = lock.lock().unwrap();
-            assert_eq!(*lock2, 1);
-            tx.send(()).unwrap();
-        });
-        rx.recv().unwrap();
-    }
-
-    #[test]
-    fn test_mutex_arc_access_in_unwind() {
-        let arc = Arc::new(Mutex::new(1));
-        let arc2 = arc.clone();
-        let _ = thread::spawn(move || -> () {
-            struct Unwinder {
-                i: Arc<Mutex<i32>>,
-            }
-            impl Drop for Unwinder {
-                fn drop(&mut self) {
-                    *self.i.lock().unwrap() += 1;
-                }
-            }
-            let _u = Unwinder { i: arc2 };
-            panic!();
-        })
-        .join();
-        let lock = arc.lock().unwrap();
-        assert_eq!(*lock, 2);
-    }
-
-    #[test]
-    fn test_mutex_unsized() {
-        let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]);
-        {
-            let b = &mut *mutex.lock().unwrap();
-            b[0] = 4;
-            b[2] = 5;
-        }
-        let comp: &[i32] = &[4, 2, 5];
-        assert_eq!(&*mutex.lock().unwrap(), comp);
-    }
-}
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
deleted file mode 100644
index 64260990824..00000000000
--- a/src/libstd/sync/once.rs
+++ /dev/null
@@ -1,690 +0,0 @@
-//! A "once initialization" primitive
-//!
-//! This primitive is meant to be used to run one-time initialization. An
-//! example use case would be for initializing an FFI library.
-
-// A "once" is a relatively simple primitive, and it's also typically provided
-// by the OS as well (see `pthread_once` or `InitOnceExecuteOnce`). The OS
-// primitives, however, tend to have surprising restrictions, such as the Unix
-// one doesn't allow an argument to be passed to the function.
-//
-// As a result, we end up implementing it ourselves in the standard library.
-// This also gives us the opportunity to optimize the implementation a bit which
-// should help the fast path on call sites. Consequently, let's explain how this
-// primitive works now!
-//
-// So to recap, the guarantees of a Once are that it will call the
-// initialization closure at most once, and it will never return until the one
-// that's running has finished running. This means that we need some form of
-// blocking here while the custom callback is running at the very least.
-// Additionally, we add on the restriction of **poisoning**. Whenever an
-// initialization closure panics, the Once enters a "poisoned" state which means
-// that all future calls will immediately panic as well.
-//
-// So to implement this, one might first reach for a `Mutex`, but those cannot
-// be put into a `static`. It also gets a lot harder with poisoning to figure
-// out when the mutex needs to be deallocated because it's not after the closure
-// finishes, but after the first successful closure finishes.
-//
-// All in all, this is instead implemented with atomics and lock-free
-// operations! Whee! Each `Once` has one word of atomic state, and this state is
-// CAS'd on to determine what to do. There are four possible state of a `Once`:
-//
-// * Incomplete - no initialization has run yet, and no thread is currently
-//                using the Once.
-// * Poisoned - some thread has previously attempted to initialize the Once, but
-//              it panicked, so the Once is now poisoned. There are no other
-//              threads currently accessing this Once.
-// * Running - some thread is currently attempting to run initialization. It may
-//             succeed, so all future threads need to wait for it to finish.
-//             Note that this state is accompanied with a payload, described
-//             below.
-// * Complete - initialization has completed and all future calls should finish
-//              immediately.
-//
-// With 4 states we need 2 bits to encode this, and we use the remaining bits
-// in the word we have allocated as a queue of threads waiting for the thread
-// responsible for entering the RUNNING state. This queue is just a linked list
-// of Waiter nodes which is monotonically increasing in size. Each node is
-// allocated on the stack, and whenever the running closure finishes it will
-// consume the entire queue and notify all waiters they should try again.
-//
-// You'll find a few more details in the implementation, but that's the gist of
-// it!
-//
-// Atomic orderings:
-// When running `Once` we deal with multiple atomics:
-// `Once.state_and_queue` and an unknown number of `Waiter.signaled`.
-// * `state_and_queue` is used (1) as a state flag, (2) for synchronizing the
-//   result of the `Once`, and (3) for synchronizing `Waiter` nodes.
-//     - At the end of the `call_inner` function we have to make sure the result
-//       of the `Once` is acquired. So every load which can be the only one to
-//       load COMPLETED must have at least Acquire ordering, which means all
-//       three of them.
-//     - `WaiterQueue::Drop` is the only place that may store COMPLETED, and
-//       must do so with Release ordering to make the result available.
-//     - `wait` inserts `Waiter` nodes as a pointer in `state_and_queue`, and
-//       needs to make the nodes available with Release ordering. The load in
-//       its `compare_and_swap` can be Relaxed because it only has to compare
-//       the atomic, not to read other data.
-//     - `WaiterQueue::Drop` must see the `Waiter` nodes, so it must load
-//       `state_and_queue` with Acquire ordering.
-//     - There is just one store where `state_and_queue` is used only as a
-//       state flag, without having to synchronize data: switching the state
-//       from INCOMPLETE to RUNNING in `call_inner`. This store can be Relaxed,
-//       but the read has to be Acquire because of the requirements mentioned
-//       above.
-// * `Waiter.signaled` is both used as a flag, and to protect a field with
-//   interior mutability in `Waiter`. `Waiter.thread` is changed in
-//   `WaiterQueue::Drop` which then sets `signaled` with Release ordering.
-//   After `wait` loads `signaled` with Acquire and sees it is true, it needs to
-//   see the changes to drop the `Waiter` struct correctly.
-// * There is one place where the two atomics `Once.state_and_queue` and
-//   `Waiter.signaled` come together, and might be reordered by the compiler or
-//   processor. Because both use Aquire ordering such a reordering is not
-//   allowed, so no need for SeqCst.
-
-use crate::cell::Cell;
-use crate::fmt;
-use crate::marker;
-use crate::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
-use crate::thread::{self, Thread};
-
-/// A synchronization primitive which can be used to run a one-time global
-/// initialization. Useful for one-time initialization for FFI or related
-/// functionality. This type can only be constructed with the [`Once::new`]
-/// constructor.
-///
-/// [`Once::new`]: struct.Once.html#method.new
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::Once;
-///
-/// static START: Once = Once::new();
-///
-/// START.call_once(|| {
-///     // run initialization here
-/// });
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Once {
-    // `state_and_queue` is actually an a pointer to a `Waiter` with extra state
-    // bits, so we add the `PhantomData` appropriately.
-    state_and_queue: AtomicUsize,
-    _marker: marker::PhantomData<*const Waiter>,
-}
-
-// The `PhantomData` of a raw pointer removes these two auto traits, but we
-// enforce both below in the implementation so this should be safe to add.
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl Sync for Once {}
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl Send for Once {}
-
-/// State yielded to [`call_once_force`]’s closure parameter. The state can be
-/// used to query the poison status of the [`Once`].
-///
-/// [`call_once_force`]: struct.Once.html#method.call_once_force
-/// [`Once`]: struct.Once.html
-#[unstable(feature = "once_poison", issue = "33577")]
-#[derive(Debug)]
-pub struct OnceState {
-    poisoned: bool,
-    set_state_on_drop_to: Cell<usize>,
-}
-
-/// Initialization value for static [`Once`] values.
-///
-/// [`Once`]: struct.Once.html
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::{Once, ONCE_INIT};
-///
-/// static START: Once = ONCE_INIT;
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_deprecated(
-    since = "1.38.0",
-    reason = "the `new` function is now preferred",
-    suggestion = "Once::new()"
-)]
-pub const ONCE_INIT: Once = Once::new();
-
-// Four states that a Once can be in, encoded into the lower bits of
-// `state_and_queue` in the Once structure.
-const INCOMPLETE: usize = 0x0;
-const POISONED: usize = 0x1;
-const RUNNING: usize = 0x2;
-const COMPLETE: usize = 0x3;
-
-// Mask to learn about the state. All other bits are the queue of waiters if
-// this is in the RUNNING state.
-const STATE_MASK: usize = 0x3;
-
-// Representation of a node in the linked list of waiters, used while in the
-// RUNNING state.
-// Note: `Waiter` can't hold a mutable pointer to the next thread, because then
-// `wait` would both hand out a mutable reference to its `Waiter` node, and keep
-// a shared reference to check `signaled`. Instead we hold shared references and
-// use interior mutability.
-#[repr(align(4))] // Ensure the two lower bits are free to use as state bits.
-struct Waiter {
-    thread: Cell<Option<Thread>>,
-    signaled: AtomicBool,
-    next: *const Waiter,
-}
-
-// Head of a linked list of waiters.
-// Every node is a struct on the stack of a waiting thread.
-// Will wake up the waiters when it gets dropped, i.e. also on panic.
-struct WaiterQueue<'a> {
-    state_and_queue: &'a AtomicUsize,
-    set_state_on_drop_to: usize,
-}
-
-impl Once {
-    /// Creates a new `Once` value.
-    #[stable(feature = "once_new", since = "1.2.0")]
-    #[rustc_const_stable(feature = "const_once_new", since = "1.32.0")]
-    pub const fn new() -> Once {
-        Once { state_and_queue: AtomicUsize::new(INCOMPLETE), _marker: marker::PhantomData }
-    }
-
-    /// Performs an initialization routine once and only once. The given closure
-    /// will be executed if this is the first time `call_once` has been called,
-    /// and otherwise the routine will *not* be invoked.
-    ///
-    /// This method will block the calling thread if another initialization
-    /// routine is currently running.
-    ///
-    /// When this function returns, it is guaranteed that some initialization
-    /// has run and completed (it may not be the closure specified). It is also
-    /// guaranteed that any memory writes performed by the executed closure can
-    /// be reliably observed by other threads at this point (there is a
-    /// happens-before relation between the closure and code executing after the
-    /// return).
-    ///
-    /// If the given closure recursively invokes `call_once` on the same `Once`
-    /// instance the exact behavior is not specified, allowed outcomes are
-    /// a panic or a deadlock.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Once;
-    ///
-    /// static mut VAL: usize = 0;
-    /// static INIT: Once = Once::new();
-    ///
-    /// // Accessing a `static mut` is unsafe much of the time, but if we do so
-    /// // in a synchronized fashion (e.g., write once or read all) then we're
-    /// // good to go!
-    /// //
-    /// // This function will only call `expensive_computation` once, and will
-    /// // otherwise always return the value returned from the first invocation.
-    /// fn get_cached_val() -> usize {
-    ///     unsafe {
-    ///         INIT.call_once(|| {
-    ///             VAL = expensive_computation();
-    ///         });
-    ///         VAL
-    ///     }
-    /// }
-    ///
-    /// fn expensive_computation() -> usize {
-    ///     // ...
-    /// # 2
-    /// }
-    /// ```
-    ///
-    /// # Panics
-    ///
-    /// The closure `f` will only be executed once if this is called
-    /// concurrently amongst many threads. If that closure panics, however, then
-    /// it will *poison* this `Once` instance, causing all future invocations of
-    /// `call_once` to also panic.
-    ///
-    /// This is similar to [poisoning with mutexes][poison].
-    ///
-    /// [poison]: struct.Mutex.html#poisoning
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn call_once<F>(&self, f: F)
-    where
-        F: FnOnce(),
-    {
-        // Fast path check
-        if self.is_completed() {
-            return;
-        }
-
-        let mut f = Some(f);
-        self.call_inner(false, &mut |_| f.take().unwrap()());
-    }
-
-    /// Performs the same function as [`call_once`] except ignores poisoning.
-    ///
-    /// Unlike [`call_once`], if this `Once` has been poisoned (i.e., a previous
-    /// call to `call_once` or `call_once_force` caused a panic), calling
-    /// `call_once_force` will still invoke the closure `f` and will _not_
-    /// result in an immediate panic. If `f` panics, the `Once` will remain
-    /// in a poison state. If `f` does _not_ panic, the `Once` will no
-    /// longer be in a poison state and all future calls to `call_once` or
-    /// `call_once_force` will be no-ops.
-    ///
-    /// The closure `f` is yielded a [`OnceState`] structure which can be used
-    /// to query the poison status of the `Once`.
-    ///
-    /// [`call_once`]: struct.Once.html#method.call_once
-    /// [`OnceState`]: struct.OnceState.html
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(once_poison)]
-    ///
-    /// use std::sync::Once;
-    /// use std::thread;
-    ///
-    /// static INIT: Once = Once::new();
-    ///
-    /// // poison the once
-    /// let handle = thread::spawn(|| {
-    ///     INIT.call_once(|| panic!());
-    /// });
-    /// assert!(handle.join().is_err());
-    ///
-    /// // poisoning propagates
-    /// let handle = thread::spawn(|| {
-    ///     INIT.call_once(|| {});
-    /// });
-    /// assert!(handle.join().is_err());
-    ///
-    /// // call_once_force will still run and reset the poisoned state
-    /// INIT.call_once_force(|state| {
-    ///     assert!(state.poisoned());
-    /// });
-    ///
-    /// // once any success happens, we stop propagating the poison
-    /// INIT.call_once(|| {});
-    /// ```
-    #[unstable(feature = "once_poison", issue = "33577")]
-    pub fn call_once_force<F>(&self, f: F)
-    where
-        F: FnOnce(&OnceState),
-    {
-        // Fast path check
-        if self.is_completed() {
-            return;
-        }
-
-        let mut f = Some(f);
-        self.call_inner(true, &mut |p| f.take().unwrap()(p));
-    }
-
-    /// Returns `true` if some `call_once` call has completed
-    /// successfully. Specifically, `is_completed` will return false in
-    /// the following situations:
-    ///   * `call_once` was not called at all,
-    ///   * `call_once` was called, but has not yet completed,
-    ///   * the `Once` instance is poisoned
-    ///
-    /// This function returning `false` does not mean that `Once` has not been
-    /// executed. For example, it may have been executed in the time between
-    /// when `is_completed` starts executing and when it returns, in which case
-    /// the `false` return value would be stale (but still permissible).
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::Once;
-    ///
-    /// static INIT: Once = Once::new();
-    ///
-    /// assert_eq!(INIT.is_completed(), false);
-    /// INIT.call_once(|| {
-    ///     assert_eq!(INIT.is_completed(), false);
-    /// });
-    /// assert_eq!(INIT.is_completed(), true);
-    /// ```
-    ///
-    /// ```
-    /// use std::sync::Once;
-    /// use std::thread;
-    ///
-    /// static INIT: Once = Once::new();
-    ///
-    /// assert_eq!(INIT.is_completed(), false);
-    /// let handle = thread::spawn(|| {
-    ///     INIT.call_once(|| panic!());
-    /// });
-    /// assert!(handle.join().is_err());
-    /// assert_eq!(INIT.is_completed(), false);
-    /// ```
-    #[stable(feature = "once_is_completed", since = "1.43.0")]
-    #[inline]
-    pub fn is_completed(&self) -> bool {
-        // An `Acquire` load is enough because that makes all the initialization
-        // operations visible to us, and, this being a fast path, weaker
-        // ordering helps with performance. This `Acquire` synchronizes with
-        // `Release` operations on the slow path.
-        self.state_and_queue.load(Ordering::Acquire) == COMPLETE
-    }
-
-    // This is a non-generic function to reduce the monomorphization cost of
-    // using `call_once` (this isn't exactly a trivial or small implementation).
-    //
-    // Additionally, this is tagged with `#[cold]` as it should indeed be cold
-    // and it helps let LLVM know that calls to this function should be off the
-    // fast path. Essentially, this should help generate more straight line code
-    // in LLVM.
-    //
-    // Finally, this takes an `FnMut` instead of a `FnOnce` because there's
-    // currently no way to take an `FnOnce` and call it via virtual dispatch
-    // without some allocation overhead.
-    #[cold]
-    fn call_inner(&self, ignore_poisoning: bool, init: &mut dyn FnMut(&OnceState)) {
-        let mut state_and_queue = self.state_and_queue.load(Ordering::Acquire);
-        loop {
-            match state_and_queue {
-                COMPLETE => break,
-                POISONED if !ignore_poisoning => {
-                    // Panic to propagate the poison.
-                    panic!("Once instance has previously been poisoned");
-                }
-                POISONED | INCOMPLETE => {
-                    // Try to register this thread as the one RUNNING.
-                    let old = self.state_and_queue.compare_and_swap(
-                        state_and_queue,
-                        RUNNING,
-                        Ordering::Acquire,
-                    );
-                    if old != state_and_queue {
-                        state_and_queue = old;
-                        continue;
-                    }
-                    // `waiter_queue` will manage other waiting threads, and
-                    // wake them up on drop.
-                    let mut waiter_queue = WaiterQueue {
-                        state_and_queue: &self.state_and_queue,
-                        set_state_on_drop_to: POISONED,
-                    };
-                    // Run the initialization function, letting it know if we're
-                    // poisoned or not.
-                    let init_state = OnceState {
-                        poisoned: state_and_queue == POISONED,
-                        set_state_on_drop_to: Cell::new(COMPLETE),
-                    };
-                    init(&init_state);
-                    waiter_queue.set_state_on_drop_to = init_state.set_state_on_drop_to.get();
-                    break;
-                }
-                _ => {
-                    // All other values must be RUNNING with possibly a
-                    // pointer to the waiter queue in the more significant bits.
-                    assert!(state_and_queue & STATE_MASK == RUNNING);
-                    wait(&self.state_and_queue, state_and_queue);
-                    state_and_queue = self.state_and_queue.load(Ordering::Acquire);
-                }
-            }
-        }
-    }
-}
-
-fn wait(state_and_queue: &AtomicUsize, mut current_state: usize) {
-    // Note: the following code was carefully written to avoid creating a
-    // mutable reference to `node` that gets aliased.
-    loop {
-        // Don't queue this thread if the status is no longer running,
-        // otherwise we will not be woken up.
-        if current_state & STATE_MASK != RUNNING {
-            return;
-        }
-
-        // Create the node for our current thread.
-        let node = Waiter {
-            thread: Cell::new(Some(thread::current())),
-            signaled: AtomicBool::new(false),
-            next: (current_state & !STATE_MASK) as *const Waiter,
-        };
-        let me = &node as *const Waiter as usize;
-
-        // Try to slide in the node at the head of the linked list, making sure
-        // that another thread didn't just replace the head of the linked list.
-        let old = state_and_queue.compare_and_swap(current_state, me | RUNNING, Ordering::Release);
-        if old != current_state {
-            current_state = old;
-            continue;
-        }
-
-        // We have enqueued ourselves, now lets wait.
-        // It is important not to return before being signaled, otherwise we
-        // would drop our `Waiter` node and leave a hole in the linked list
-        // (and a dangling reference). Guard against spurious wakeups by
-        // reparking ourselves until we are signaled.
-        while !node.signaled.load(Ordering::Acquire) {
-            // If the managing thread happens to signal and unpark us before we
-            // can park ourselves, the result could be this thread never gets
-            // unparked. Luckily `park` comes with the guarantee that if it got
-            // an `unpark` just before on an unparked thread is does not park.
-            thread::park();
-        }
-        break;
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl fmt::Debug for Once {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.pad("Once { .. }")
-    }
-}
-
-impl Drop for WaiterQueue<'_> {
-    fn drop(&mut self) {
-        // Swap out our state with however we finished.
-        let state_and_queue =
-            self.state_and_queue.swap(self.set_state_on_drop_to, Ordering::AcqRel);
-
-        // We should only ever see an old state which was RUNNING.
-        assert_eq!(state_and_queue & STATE_MASK, RUNNING);
-
-        // Walk the entire linked list of waiters and wake them up (in lifo
-        // order, last to register is first to wake up).
-        unsafe {
-            // Right after setting `node.signaled = true` the other thread may
-            // free `node` if there happens to be has a spurious wakeup.
-            // So we have to take out the `thread` field and copy the pointer to
-            // `next` first.
-            let mut queue = (state_and_queue & !STATE_MASK) as *const Waiter;
-            while !queue.is_null() {
-                let next = (*queue).next;
-                let thread = (*queue).thread.take().unwrap();
-                (*queue).signaled.store(true, Ordering::Release);
-                // ^- FIXME (maybe): This is another case of issue #55005
-                // `store()` has a potentially dangling ref to `signaled`.
-                queue = next;
-                thread.unpark();
-            }
-        }
-    }
-}
-
-impl OnceState {
-    /// Returns `true` if the associated [`Once`] was poisoned prior to the
-    /// invocation of the closure passed to [`call_once_force`].
-    ///
-    /// [`call_once_force`]: struct.Once.html#method.call_once_force
-    /// [`Once`]: struct.Once.html
-    ///
-    /// # Examples
-    ///
-    /// A poisoned `Once`:
-    ///
-    /// ```
-    /// #![feature(once_poison)]
-    ///
-    /// use std::sync::Once;
-    /// use std::thread;
-    ///
-    /// static INIT: Once = Once::new();
-    ///
-    /// // poison the once
-    /// let handle = thread::spawn(|| {
-    ///     INIT.call_once(|| panic!());
-    /// });
-    /// assert!(handle.join().is_err());
-    ///
-    /// INIT.call_once_force(|state| {
-    ///     assert!(state.poisoned());
-    /// });
-    /// ```
-    ///
-    /// An unpoisoned `Once`:
-    ///
-    /// ```
-    /// #![feature(once_poison)]
-    ///
-    /// use std::sync::Once;
-    ///
-    /// static INIT: Once = Once::new();
-    ///
-    /// INIT.call_once_force(|state| {
-    ///     assert!(!state.poisoned());
-    /// });
-    #[unstable(feature = "once_poison", issue = "33577")]
-    pub fn poisoned(&self) -> bool {
-        self.poisoned
-    }
-
-    /// Poison the associated [`Once`] without explicitly panicking.
-    ///
-    /// [`Once`]: struct.Once.html
-    // NOTE: This is currently only exposed for the `lazy` module
-    pub(crate) fn poison(&self) {
-        self.set_state_on_drop_to.set(POISONED);
-    }
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod tests {
-    use super::Once;
-    use crate::panic;
-    use crate::sync::mpsc::channel;
-    use crate::thread;
-
-    #[test]
-    fn smoke_once() {
-        static O: Once = Once::new();
-        let mut a = 0;
-        O.call_once(|| a += 1);
-        assert_eq!(a, 1);
-        O.call_once(|| a += 1);
-        assert_eq!(a, 1);
-    }
-
-    #[test]
-    fn stampede_once() {
-        static O: Once = Once::new();
-        static mut RUN: bool = false;
-
-        let (tx, rx) = channel();
-        for _ in 0..10 {
-            let tx = tx.clone();
-            thread::spawn(move || {
-                for _ in 0..4 {
-                    thread::yield_now()
-                }
-                unsafe {
-                    O.call_once(|| {
-                        assert!(!RUN);
-                        RUN = true;
-                    });
-                    assert!(RUN);
-                }
-                tx.send(()).unwrap();
-            });
-        }
-
-        unsafe {
-            O.call_once(|| {
-                assert!(!RUN);
-                RUN = true;
-            });
-            assert!(RUN);
-        }
-
-        for _ in 0..10 {
-            rx.recv().unwrap();
-        }
-    }
-
-    #[test]
-    fn poison_bad() {
-        static O: Once = Once::new();
-
-        // poison the once
-        let t = panic::catch_unwind(|| {
-            O.call_once(|| panic!());
-        });
-        assert!(t.is_err());
-
-        // poisoning propagates
-        let t = panic::catch_unwind(|| {
-            O.call_once(|| {});
-        });
-        assert!(t.is_err());
-
-        // we can subvert poisoning, however
-        let mut called = false;
-        O.call_once_force(|p| {
-            called = true;
-            assert!(p.poisoned())
-        });
-        assert!(called);
-
-        // once any success happens, we stop propagating the poison
-        O.call_once(|| {});
-    }
-
-    #[test]
-    fn wait_for_force_to_finish() {
-        static O: Once = Once::new();
-
-        // poison the once
-        let t = panic::catch_unwind(|| {
-            O.call_once(|| panic!());
-        });
-        assert!(t.is_err());
-
-        // make sure someone's waiting inside the once via a force
-        let (tx1, rx1) = channel();
-        let (tx2, rx2) = channel();
-        let t1 = thread::spawn(move || {
-            O.call_once_force(|p| {
-                assert!(p.poisoned());
-                tx1.send(()).unwrap();
-                rx2.recv().unwrap();
-            });
-        });
-
-        rx1.recv().unwrap();
-
-        // put another waiter on the once
-        let t2 = thread::spawn(|| {
-            let mut called = false;
-            O.call_once(|| {
-                called = true;
-            });
-            assert!(!called);
-        });
-
-        tx2.send(()).unwrap();
-
-        assert!(t1.join().is_ok());
-        assert!(t2.join().is_ok());
-    }
-}
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
deleted file mode 100644
index 50f54dbf143..00000000000
--- a/src/libstd/sync/rwlock.rs
+++ /dev/null
@@ -1,799 +0,0 @@
-use crate::cell::UnsafeCell;
-use crate::fmt;
-use crate::mem;
-use crate::ops::{Deref, DerefMut};
-use crate::ptr;
-use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
-use crate::sys_common::rwlock as sys;
-
-/// A reader-writer lock
-///
-/// This type of lock allows a number of readers or at most one writer at any
-/// point in time. The write portion of this lock typically allows modification
-/// of the underlying data (exclusive access) and the read portion of this lock
-/// typically allows for read-only access (shared access).
-///
-/// In comparison, a [`Mutex`] does not distinguish between readers or writers
-/// that acquire the lock, therefore blocking any threads waiting for the lock to
-/// become available. An `RwLock` will allow any number of readers to acquire the
-/// lock as long as a writer is not holding the lock.
-///
-/// The priority policy of the lock is dependent on the underlying operating
-/// system's implementation, and this type does not guarantee that any
-/// particular policy will be used.
-///
-/// The type parameter `T` represents the data that this lock protects. It is
-/// required that `T` satisfies [`Send`] to be shared across threads and
-/// [`Sync`] to allow concurrent access through readers. The RAII guards
-/// returned from the locking methods implement [`Deref`] (and [`DerefMut`]
-/// for the `write` methods) to allow access to the content of the lock.
-///
-/// # Poisoning
-///
-/// An `RwLock`, like [`Mutex`], will become poisoned on a panic. Note, however,
-/// that an `RwLock` may only be poisoned if a panic occurs while it is locked
-/// exclusively (write mode). If a panic occurs in any reader, then the lock
-/// will not be poisoned.
-///
-/// # Examples
-///
-/// ```
-/// use std::sync::RwLock;
-///
-/// let lock = RwLock::new(5);
-///
-/// // many reader locks can be held at once
-/// {
-///     let r1 = lock.read().unwrap();
-///     let r2 = lock.read().unwrap();
-///     assert_eq!(*r1, 5);
-///     assert_eq!(*r2, 5);
-/// } // read locks are dropped at this point
-///
-/// // only one write lock may be held, however
-/// {
-///     let mut w = lock.write().unwrap();
-///     *w += 1;
-///     assert_eq!(*w, 6);
-/// } // write lock is dropped here
-/// ```
-///
-/// [`Deref`]: ../../std/ops/trait.Deref.html
-/// [`DerefMut`]: ../../std/ops/trait.DerefMut.html
-/// [`Send`]: ../../std/marker/trait.Send.html
-/// [`Sync`]: ../../std/marker/trait.Sync.html
-/// [`Mutex`]: struct.Mutex.html
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct RwLock<T: ?Sized> {
-    inner: Box<sys::RWLock>,
-    poison: poison::Flag,
-    data: UnsafeCell<T>,
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Send> Send for RwLock<T> {}
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}
-
-/// RAII structure used to release the shared read access of a lock when
-/// dropped.
-///
-/// This structure is created by the [`read`] and [`try_read`] methods on
-/// [`RwLock`].
-///
-/// [`read`]: struct.RwLock.html#method.read
-/// [`try_read`]: struct.RwLock.html#method.try_read
-/// [`RwLock`]: struct.RwLock.html
-#[must_use = "if unused the RwLock will immediately unlock"]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct RwLockReadGuard<'a, T: ?Sized + 'a> {
-    lock: &'a RwLock<T>,
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> !Send for RwLockReadGuard<'_, T> {}
-
-#[stable(feature = "rwlock_guard_sync", since = "1.23.0")]
-unsafe impl<T: ?Sized + Sync> Sync for RwLockReadGuard<'_, T> {}
-
-/// RAII structure used to release the exclusive write access of a lock when
-/// dropped.
-///
-/// This structure is created by the [`write`] and [`try_write`] methods
-/// on [`RwLock`].
-///
-/// [`write`]: struct.RwLock.html#method.write
-/// [`try_write`]: struct.RwLock.html#method.try_write
-/// [`RwLock`]: struct.RwLock.html
-#[must_use = "if unused the RwLock will immediately unlock"]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct RwLockWriteGuard<'a, T: ?Sized + 'a> {
-    lock: &'a RwLock<T>,
-    poison: poison::Guard,
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> !Send for RwLockWriteGuard<'_, T> {}
-
-#[stable(feature = "rwlock_guard_sync", since = "1.23.0")]
-unsafe impl<T: ?Sized + Sync> Sync for RwLockWriteGuard<'_, T> {}
-
-impl<T> RwLock<T> {
-    /// Creates a new instance of an `RwLock<T>` which is unlocked.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::RwLock;
-    ///
-    /// let lock = RwLock::new(5);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new(t: T) -> RwLock<T> {
-        RwLock {
-            inner: box sys::RWLock::new(),
-            poison: poison::Flag::new(),
-            data: UnsafeCell::new(t),
-        }
-    }
-}
-
-impl<T: ?Sized> RwLock<T> {
-    /// Locks this rwlock with shared read access, blocking the current thread
-    /// until it can be acquired.
-    ///
-    /// The calling thread will be blocked until there are no more writers which
-    /// hold the lock. There may be other readers currently inside the lock when
-    /// this method returns. This method does not provide any guarantees with
-    /// respect to the ordering of whether contentious readers or writers will
-    /// acquire the lock first.
-    ///
-    /// Returns an RAII guard which will release this thread's shared access
-    /// once it is dropped.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock.
-    /// The failure will occur immediately after the lock has been acquired.
-    ///
-    /// # Panics
-    ///
-    /// This function might panic when called if the lock is already held by the current thread.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, RwLock};
-    /// use std::thread;
-    ///
-    /// let lock = Arc::new(RwLock::new(1));
-    /// let c_lock = lock.clone();
-    ///
-    /// let n = lock.read().unwrap();
-    /// assert_eq!(*n, 1);
-    ///
-    /// thread::spawn(move || {
-    ///     let r = c_lock.read();
-    ///     assert!(r.is_ok());
-    /// }).join().unwrap();
-    /// ```
-    #[inline]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn read(&self) -> LockResult<RwLockReadGuard<'_, T>> {
-        unsafe {
-            self.inner.read();
-            RwLockReadGuard::new(self)
-        }
-    }
-
-    /// Attempts to acquire this rwlock with shared read access.
-    ///
-    /// If the access could not be granted at this time, then `Err` is returned.
-    /// Otherwise, an RAII guard is returned which will release the shared access
-    /// when it is dropped.
-    ///
-    /// This function does not block.
-    ///
-    /// This function does not provide any guarantees with respect to the ordering
-    /// of whether contentious readers or writers will acquire the lock first.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::RwLock;
-    ///
-    /// let lock = RwLock::new(1);
-    ///
-    /// match lock.try_read() {
-    ///     Ok(n) => assert_eq!(*n, 1),
-    ///     Err(_) => unreachable!(),
-    /// };
-    /// ```
-    #[inline]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<'_, T>> {
-        unsafe {
-            if self.inner.try_read() {
-                Ok(RwLockReadGuard::new(self)?)
-            } else {
-                Err(TryLockError::WouldBlock)
-            }
-        }
-    }
-
-    /// Locks this rwlock with exclusive write access, blocking the current
-    /// thread until it can be acquired.
-    ///
-    /// This function will not return while other writers or other readers
-    /// currently have access to the lock.
-    ///
-    /// Returns an RAII guard which will drop the write access of this rwlock
-    /// when dropped.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock.
-    /// An error will be returned when the lock is acquired.
-    ///
-    /// # Panics
-    ///
-    /// This function might panic when called if the lock is already held by the current thread.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::RwLock;
-    ///
-    /// let lock = RwLock::new(1);
-    ///
-    /// let mut n = lock.write().unwrap();
-    /// *n = 2;
-    ///
-    /// assert!(lock.try_read().is_err());
-    /// ```
-    #[inline]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn write(&self) -> LockResult<RwLockWriteGuard<'_, T>> {
-        unsafe {
-            self.inner.write();
-            RwLockWriteGuard::new(self)
-        }
-    }
-
-    /// Attempts to lock this rwlock with exclusive write access.
-    ///
-    /// If the lock could not be acquired at this time, then `Err` is returned.
-    /// Otherwise, an RAII guard is returned which will release the lock when
-    /// it is dropped.
-    ///
-    /// This function does not block.
-    ///
-    /// This function does not provide any guarantees with respect to the ordering
-    /// of whether contentious readers or writers will acquire the lock first.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::RwLock;
-    ///
-    /// let lock = RwLock::new(1);
-    ///
-    /// let n = lock.read().unwrap();
-    /// assert_eq!(*n, 1);
-    ///
-    /// assert!(lock.try_write().is_err());
-    /// ```
-    #[inline]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<'_, T>> {
-        unsafe {
-            if self.inner.try_write() {
-                Ok(RwLockWriteGuard::new(self)?)
-            } else {
-                Err(TryLockError::WouldBlock)
-            }
-        }
-    }
-
-    /// Determines whether the lock is poisoned.
-    ///
-    /// If another thread is active, the lock can still become poisoned at any
-    /// time. You should not trust a `false` value for program correctness
-    /// without additional synchronization.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::{Arc, RwLock};
-    /// use std::thread;
-    ///
-    /// let lock = Arc::new(RwLock::new(0));
-    /// let c_lock = lock.clone();
-    ///
-    /// let _ = thread::spawn(move || {
-    ///     let _lock = c_lock.write().unwrap();
-    ///     panic!(); // the lock gets poisoned
-    /// }).join();
-    /// assert_eq!(lock.is_poisoned(), true);
-    /// ```
-    #[inline]
-    #[stable(feature = "sync_poison", since = "1.2.0")]
-    pub fn is_poisoned(&self) -> bool {
-        self.poison.get()
-    }
-
-    /// Consumes this `RwLock`, returning the underlying data.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::RwLock;
-    ///
-    /// let lock = RwLock::new(String::new());
-    /// {
-    ///     let mut s = lock.write().unwrap();
-    ///     *s = "modified".to_owned();
-    /// }
-    /// assert_eq!(lock.into_inner().unwrap(), "modified");
-    /// ```
-    #[stable(feature = "rwlock_into_inner", since = "1.6.0")]
-    pub fn into_inner(self) -> LockResult<T>
-    where
-        T: Sized,
-    {
-        // We know statically that there are no outstanding references to
-        // `self` so there's no need to lock the inner lock.
-        //
-        // To get the inner value, we'd like to call `data.into_inner()`,
-        // but because `RwLock` impl-s `Drop`, we can't move out of it, so
-        // we'll have to destructure it manually instead.
-        unsafe {
-            // Like `let RwLock { inner, poison, data } = self`.
-            let (inner, poison, data) = {
-                let RwLock { ref inner, ref poison, ref data } = self;
-                (ptr::read(inner), ptr::read(poison), ptr::read(data))
-            };
-            mem::forget(self);
-            inner.destroy(); // Keep in sync with the `Drop` impl.
-            drop(inner);
-
-            poison::map_result(poison.borrow(), |_| data.into_inner())
-        }
-    }
-
-    /// Returns a mutable reference to the underlying data.
-    ///
-    /// Since this call borrows the `RwLock` mutably, no actual locking needs to
-    /// take place -- the mutable borrow statically guarantees no locks exist.
-    ///
-    /// # Errors
-    ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::sync::RwLock;
-    ///
-    /// let mut lock = RwLock::new(0);
-    /// *lock.get_mut().unwrap() = 10;
-    /// assert_eq!(*lock.read().unwrap(), 10);
-    /// ```
-    #[stable(feature = "rwlock_get_mut", since = "1.6.0")]
-    pub fn get_mut(&mut self) -> LockResult<&mut T> {
-        // We know statically that there are no other references to `self`, so
-        // there's no need to lock the inner lock.
-        let data = unsafe { &mut *self.data.get() };
-        poison::map_result(self.poison.borrow(), |_| data)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<#[may_dangle] T: ?Sized> Drop for RwLock<T> {
-    fn drop(&mut self) {
-        // IMPORTANT: This code needs to be kept in sync with `RwLock::into_inner`.
-        unsafe { self.inner.destroy() }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.try_read() {
-            Ok(guard) => f.debug_struct("RwLock").field("data", &&*guard).finish(),
-            Err(TryLockError::Poisoned(err)) => {
-                f.debug_struct("RwLock").field("data", &&**err.get_ref()).finish()
-            }
-            Err(TryLockError::WouldBlock) => {
-                struct LockedPlaceholder;
-                impl fmt::Debug for LockedPlaceholder {
-                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                        f.write_str("<locked>")
-                    }
-                }
-
-                f.debug_struct("RwLock").field("data", &LockedPlaceholder).finish()
-            }
-        }
-    }
-}
-
-#[stable(feature = "rw_lock_default", since = "1.10.0")]
-impl<T: Default> Default for RwLock<T> {
-    /// Creates a new `RwLock<T>`, with the `Default` value for T.
-    fn default() -> RwLock<T> {
-        RwLock::new(Default::default())
-    }
-}
-
-#[stable(feature = "rw_lock_from", since = "1.24.0")]
-impl<T> From<T> for RwLock<T> {
-    /// Creates a new instance of an `RwLock<T>` which is unlocked.
-    /// This is equivalent to [`RwLock::new`].
-    ///
-    /// [`RwLock::new`]: ../../std/sync/struct.RwLock.html#method.new
-    fn from(t: T) -> Self {
-        RwLock::new(t)
-    }
-}
-
-impl<'rwlock, T: ?Sized> RwLockReadGuard<'rwlock, T> {
-    unsafe fn new(lock: &'rwlock RwLock<T>) -> LockResult<RwLockReadGuard<'rwlock, T>> {
-        poison::map_result(lock.poison.borrow(), |_| RwLockReadGuard { lock })
-    }
-}
-
-impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
-    unsafe fn new(lock: &'rwlock RwLock<T>) -> LockResult<RwLockWriteGuard<'rwlock, T>> {
-        poison::map_result(lock.poison.borrow(), |guard| RwLockWriteGuard { lock, poison: guard })
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl<T: fmt::Debug> fmt::Debug for RwLockReadGuard<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("RwLockReadGuard").field("lock", &self.lock).finish()
-    }
-}
-
-#[stable(feature = "std_guard_impls", since = "1.20.0")]
-impl<T: ?Sized + fmt::Display> fmt::Display for RwLockReadGuard<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        (**self).fmt(f)
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl<T: fmt::Debug> fmt::Debug for RwLockWriteGuard<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("RwLockWriteGuard").field("lock", &self.lock).finish()
-    }
-}
-
-#[stable(feature = "std_guard_impls", since = "1.20.0")]
-impl<T: ?Sized + fmt::Display> fmt::Display for RwLockWriteGuard<'_, T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        (**self).fmt(f)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Deref for RwLockReadGuard<'_, T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        unsafe { &*self.lock.data.get() }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Deref for RwLockWriteGuard<'_, T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        unsafe { &*self.lock.data.get() }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> DerefMut for RwLockWriteGuard<'_, T> {
-    fn deref_mut(&mut self) -> &mut T {
-        unsafe { &mut *self.lock.data.get() }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Drop for RwLockReadGuard<'_, T> {
-    fn drop(&mut self) {
-        unsafe {
-            self.lock.inner.read_unlock();
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Drop for RwLockWriteGuard<'_, T> {
-    fn drop(&mut self) {
-        self.lock.poison.done(&self.poison);
-        unsafe {
-            self.lock.inner.write_unlock();
-        }
-    }
-}
-
-#[cfg(all(test, not(target_os = "emscripten")))]
-mod tests {
-    use crate::sync::atomic::{AtomicUsize, Ordering};
-    use crate::sync::mpsc::channel;
-    use crate::sync::{Arc, RwLock, TryLockError};
-    use crate::thread;
-    use rand::{self, Rng};
-
-    #[derive(Eq, PartialEq, Debug)]
-    struct NonCopy(i32);
-
-    #[test]
-    fn smoke() {
-        let l = RwLock::new(());
-        drop(l.read().unwrap());
-        drop(l.write().unwrap());
-        drop((l.read().unwrap(), l.read().unwrap()));
-        drop(l.write().unwrap());
-    }
-
-    #[test]
-    fn frob() {
-        const N: u32 = 10;
-        const M: usize = 1000;
-
-        let r = Arc::new(RwLock::new(()));
-
-        let (tx, rx) = channel::<()>();
-        for _ in 0..N {
-            let tx = tx.clone();
-            let r = r.clone();
-            thread::spawn(move || {
-                let mut rng = rand::thread_rng();
-                for _ in 0..M {
-                    if rng.gen_bool(1.0 / (N as f64)) {
-                        drop(r.write().unwrap());
-                    } else {
-                        drop(r.read().unwrap());
-                    }
-                }
-                drop(tx);
-            });
-        }
-        drop(tx);
-        let _ = rx.recv();
-    }
-
-    #[test]
-    fn test_rw_arc_poison_wr() {
-        let arc = Arc::new(RwLock::new(1));
-        let arc2 = arc.clone();
-        let _: Result<(), _> = thread::spawn(move || {
-            let _lock = arc2.write().unwrap();
-            panic!();
-        })
-        .join();
-        assert!(arc.read().is_err());
-    }
-
-    #[test]
-    fn test_rw_arc_poison_ww() {
-        let arc = Arc::new(RwLock::new(1));
-        assert!(!arc.is_poisoned());
-        let arc2 = arc.clone();
-        let _: Result<(), _> = thread::spawn(move || {
-            let _lock = arc2.write().unwrap();
-            panic!();
-        })
-        .join();
-        assert!(arc.write().is_err());
-        assert!(arc.is_poisoned());
-    }
-
-    #[test]
-    fn test_rw_arc_no_poison_rr() {
-        let arc = Arc::new(RwLock::new(1));
-        let arc2 = arc.clone();
-        let _: Result<(), _> = thread::spawn(move || {
-            let _lock = arc2.read().unwrap();
-            panic!();
-        })
-        .join();
-        let lock = arc.read().unwrap();
-        assert_eq!(*lock, 1);
-    }
-    #[test]
-    fn test_rw_arc_no_poison_rw() {
-        let arc = Arc::new(RwLock::new(1));
-        let arc2 = arc.clone();
-        let _: Result<(), _> = thread::spawn(move || {
-            let _lock = arc2.read().unwrap();
-            panic!()
-        })
-        .join();
-        let lock = arc.write().unwrap();
-        assert_eq!(*lock, 1);
-    }
-
-    #[test]
-    fn test_rw_arc() {
-        let arc = Arc::new(RwLock::new(0));
-        let arc2 = arc.clone();
-        let (tx, rx) = channel();
-
-        thread::spawn(move || {
-            let mut lock = arc2.write().unwrap();
-            for _ in 0..10 {
-                let tmp = *lock;
-                *lock = -1;
-                thread::yield_now();
-                *lock = tmp + 1;
-            }
-            tx.send(()).unwrap();
-        });
-
-        // Readers try to catch the writer in the act
-        let mut children = Vec::new();
-        for _ in 0..5 {
-            let arc3 = arc.clone();
-            children.push(thread::spawn(move || {
-                let lock = arc3.read().unwrap();
-                assert!(*lock >= 0);
-            }));
-        }
-
-        // Wait for children to pass their asserts
-        for r in children {
-            assert!(r.join().is_ok());
-        }
-
-        // Wait for writer to finish
-        rx.recv().unwrap();
-        let lock = arc.read().unwrap();
-        assert_eq!(*lock, 10);
-    }
-
-    #[test]
-    fn test_rw_arc_access_in_unwind() {
-        let arc = Arc::new(RwLock::new(1));
-        let arc2 = arc.clone();
-        let _ = thread::spawn(move || -> () {
-            struct Unwinder {
-                i: Arc<RwLock<isize>>,
-            }
-            impl Drop for Unwinder {
-                fn drop(&mut self) {
-                    let mut lock = self.i.write().unwrap();
-                    *lock += 1;
-                }
-            }
-            let _u = Unwinder { i: arc2 };
-            panic!();
-        })
-        .join();
-        let lock = arc.read().unwrap();
-        assert_eq!(*lock, 2);
-    }
-
-    #[test]
-    fn test_rwlock_unsized() {
-        let rw: &RwLock<[i32]> = &RwLock::new([1, 2, 3]);
-        {
-            let b = &mut *rw.write().unwrap();
-            b[0] = 4;
-            b[2] = 5;
-        }
-        let comp: &[i32] = &[4, 2, 5];
-        assert_eq!(&*rw.read().unwrap(), comp);
-    }
-
-    #[test]
-    fn test_rwlock_try_write() {
-        let lock = RwLock::new(0isize);
-        let read_guard = lock.read().unwrap();
-
-        let write_result = lock.try_write();
-        match write_result {
-            Err(TryLockError::WouldBlock) => (),
-            Ok(_) => assert!(false, "try_write should not succeed while read_guard is in scope"),
-            Err(_) => assert!(false, "unexpected error"),
-        }
-
-        drop(read_guard);
-    }
-
-    #[test]
-    fn test_into_inner() {
-        let m = RwLock::new(NonCopy(10));
-        assert_eq!(m.into_inner().unwrap(), NonCopy(10));
-    }
-
-    #[test]
-    fn test_into_inner_drop() {
-        struct Foo(Arc<AtomicUsize>);
-        impl Drop for Foo {
-            fn drop(&mut self) {
-                self.0.fetch_add(1, Ordering::SeqCst);
-            }
-        }
-        let num_drops = Arc::new(AtomicUsize::new(0));
-        let m = RwLock::new(Foo(num_drops.clone()));
-        assert_eq!(num_drops.load(Ordering::SeqCst), 0);
-        {
-            let _inner = m.into_inner().unwrap();
-            assert_eq!(num_drops.load(Ordering::SeqCst), 0);
-        }
-        assert_eq!(num_drops.load(Ordering::SeqCst), 1);
-    }
-
-    #[test]
-    fn test_into_inner_poison() {
-        let m = Arc::new(RwLock::new(NonCopy(10)));
-        let m2 = m.clone();
-        let _ = thread::spawn(move || {
-            let _lock = m2.write().unwrap();
-            panic!("test panic in inner thread to poison RwLock");
-        })
-        .join();
-
-        assert!(m.is_poisoned());
-        match Arc::try_unwrap(m).unwrap().into_inner() {
-            Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
-            Ok(x) => panic!("into_inner of poisoned RwLock is Ok: {:?}", x),
-        }
-    }
-
-    #[test]
-    fn test_get_mut() {
-        let mut m = RwLock::new(NonCopy(10));
-        *m.get_mut().unwrap() = NonCopy(20);
-        assert_eq!(m.into_inner().unwrap(), NonCopy(20));
-    }
-
-    #[test]
-    fn test_get_mut_poison() {
-        let m = Arc::new(RwLock::new(NonCopy(10)));
-        let m2 = m.clone();
-        let _ = thread::spawn(move || {
-            let _lock = m2.write().unwrap();
-            panic!("test panic in inner thread to poison RwLock");
-        })
-        .join();
-
-        assert!(m.is_poisoned());
-        match Arc::try_unwrap(m).unwrap().get_mut() {
-            Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
-            Ok(x) => panic!("get_mut of poisoned RwLock is Ok: {:?}", x),
-        }
-    }
-}